In both 2nd Peter 3:15 and 16, Peter is referring to their copies of Paul's writings - to their[/B version of our "all for us, but not all to us, nor all about us."
2 Peter 3:
1. This second epistle, beloved, I now write unto you; in both which I stir up your pure minds by way of remembrance:
2. That ye may be mindful of the words which were spoken before by the holy prophets, and of the commandment of us the apostles of the Lord and Saviour:
3. Knowing this first, that there shall come in the last days scoffers, walking after their own lusts,
4. And saying, Where is the promise of his coming? for since the fathers fell asleep, all things continue as they were from the beginning of the creation.
9. The Lord is not slack concerning his promise, as some men count slackness; but is longsuffering to us-ward, not willing that any should perish, but that all should come to repentance.
14. Wherefore, beloved, seeing that ye look for such things, be diligent that ye may be found of him in peace, without spot, and blameless.
15. And account that the longsuffering of our Lord is salvation; even as our beloved brother Paul also according to the wisdom given unto him hath written unto you;
In what sense had Paul also, according to the wisdom given unto him, written unto them?
16. As also in all his epistles, speaking in them of these things; in which are some things hard to be understood, which they that are unlearned and unstable wrest, as they do also the other scriptures, unto their own destruction.
Romans, for example, "as also, in all his epistles," were for them, but not to them, nor about them - Romans 9, for example, as to this delay in the Lord's 2nd Advent return:
22. What if God, willing to shew his wrath, and to make his power known, endured with much longsuffering the vessels of wrath fitted to destruction:
23. And that he might make known the riches of his glory on the vessels of mercy, which he had afore prepared unto glory,
24. Even us, whom he hath called, not of the Jews only, but also of the Gentiles?
Romans is the first in the order of Paul's Epistles as to "instruction in righteousness," "rightly divided," 2 Timothy 2:15; 3:16, 17.
Romans contains much of both ours and their version of "all for us, not all to us, nor about us."
Romans 11:25-29 is for us, but is about them, for example - the delay in the Lord's return.
Which delay began with what? His all longsuffering - 1 Timothy 1:
16. Howbeit for this cause I obtained mercy, that in me first Jesus Christ might shew forth all longsuffering, for a pattern to them which should hereafter believe on him to life everlasting.
What's that about? How that God "would have all men to be saved, and to come unto the knowledge of the truth" 1 Timothy 2:4.
This is not the "many" of Israel - this is the "all men" of Paul's distinct - Acts 17:
30. And the times of this ignorance God winked at; but now commandeth all men every where to repent:
31. Because he hath appointed a day, in the which he will judge the world in righteousness by that man whom he hath ordained; whereof he hath given assurance unto all men, in that he hath raised him from the dead.
Romans 2:
16. In the day when God shall judge the secrets of men by Jesus Christ according to my gospel.
In other words - the Resurrection of Christ had a Two-Fold Purpose: Prophecy and Mystery.
Israel's Prophesied salvation and fulness of their blessing over the Gentiles; Romans 15:8-12.
And the Body's Kept Secret salvation and fulness of its blessing over all creation, Romans 8.
Both based on the Cross of Christ, 2 Timothy 2:
8. Remember that Jesus Christ of the seed of David was raised from the dead according to my gospel:
9. Wherein I suffer trouble, as an evil doer, even unto bonds; but the word of God is not bound.
The one - concerning proving He is the seed of David by the resurrection from the dead - had been Prophesied.
The other - His resurrection form the dead according to Paul's gospel towards the glory of the Lord in a New Creature had been Kept Secret since the world began.
The Adversary had had not problem offering the Lord the kingdoms of this world, Matthew 4.
For he and his dark princes would still have those fallen places in the Heavenlies to traffic in their iniquity from, Ephesians. 6.
Little did he know that despite the sum his wisdom as to God's Prophesied wisdom had been, God had a hidden wisdom.
Which, had they known it, would not have crucified the Lord of this hidden wisdom's glory, 2 Corinthians 2.
Which hidden wisdom we can now know the manifold aspects of as to this New Creature by which the Son will fill all authority in all creation by - Ephesians 1:
18. The eyes of your understanding being enlightened; that ye may know what is the hope of his calling, and what the riches of the glory of his inheritance in the saints,
19. And what is the exceeding greatness of his power to us-ward who believe, according to the working of his mighty power,
20. Which he wrought in Christ, when he raised him from the dead, and set him at his own right hand in the heavenly places,
21. Far above all principality, and power, and might, and dominion, and every name that is named, not only in this world, but also in that which is to come:
22. And hath put all things under his feet, and gave him to be the head over all things to the church,
23. Which is his body, the fulness of him that filleth all in all.
Jesus Christ - "Of whom the whole family in heaven and earth is named," Ephesians 3:15.
Jesus Christ - His resurrection from the dead proving He is the Son of God; the Christ; the King of Israel over all the Earth - David's Prophesied heir, Romans 1.
Jesus Christ - He is resurrection from the dead also proving He is the Head of a New Creature far above all principalities in the Heavenlies, 2 Timothy 2.
Ephesians 3:
10. To the intent that now unto the principalities and powers in heavenly places might be known by the church the manifold wisdom of God,
11. According to the eternal purpose which he purposed in Christ Jesus our Lord:
12. In whom we have boldness and access with confidence by the faith of him.
As J.C. O'Hair had so well noted in that article on verse 10's "now" - that now is found from Paul's salvation on the road to Damascus forward...
2 Peter 3:
1. This second epistle, beloved, I now write unto you; in both which I stir up your pure minds by way of remembrance:
2. That ye may be mindful of the words which were spoken before by the holy prophets, and of the commandment of us the apostles of the Lord and Saviour:
3. Knowing this first, that there shall come in the last days scoffers, walking after their own lusts,
4. And saying, Where is the promise of his coming? for since the fathers fell asleep, all things continue as they were from the beginning of the creation.
9. The Lord is not slack concerning his promise, as some men count slackness; but is longsuffering to us-ward, not willing that any should perish, but that all should come to repentance.
14. Wherefore, beloved, seeing that ye look for such things, be diligent that ye may be found of him in peace, without spot, and blameless.
15. And account that the longsuffering of our Lord is salvation; even as our beloved brother Paul also according to the wisdom given unto him hath written unto you;
In what sense had Paul also, according to the wisdom given unto him, written unto them?
16. As also in all his epistles, speaking in them of these things; in which are some things hard to be understood, which they that are unlearned and unstable wrest, as they do also the other scriptures, unto their own destruction.
Romans, for example, "as also, in all his epistles," were for them, but not to them, nor about them - Romans 9, for example, as to this delay in the Lord's 2nd Advent return:
22. What if God, willing to shew his wrath, and to make his power known, endured with much longsuffering the vessels of wrath fitted to destruction:
23. And that he might make known the riches of his glory on the vessels of mercy, which he had afore prepared unto glory,
24. Even us, whom he hath called, not of the Jews only, but also of the Gentiles?
Romans is the first in the order of Paul's Epistles as to "instruction in righteousness," "rightly divided," 2 Timothy 2:15; 3:16, 17.
Romans contains much of both ours and their version of "all for us, not all to us, nor about us."
Romans 11:25-29 is for us, but is about them, for example - the delay in the Lord's return.
Which delay began with what? His all longsuffering - 1 Timothy 1:
16. Howbeit for this cause I obtained mercy, that in me first Jesus Christ might shew forth all longsuffering, for a pattern to them which should hereafter believe on him to life everlasting.
What's that about? How that God "would have all men to be saved, and to come unto the knowledge of the truth" 1 Timothy 2:4.
This is not the "many" of Israel - this is the "all men" of Paul's distinct - Acts 17:
30. And the times of this ignorance God winked at; but now commandeth all men every where to repent:
31. Because he hath appointed a day, in the which he will judge the world in righteousness by that man whom he hath ordained; whereof he hath given assurance unto all men, in that he hath raised him from the dead.
Romans 2:
16. In the day when God shall judge the secrets of men by Jesus Christ according to my gospel.
In other words - the Resurrection of Christ had a Two-Fold Purpose: Prophecy and Mystery.
Israel's Prophesied salvation and fulness of their blessing over the Gentiles; Romans 15:8-12.
And the Body's Kept Secret salvation and fulness of its blessing over all creation, Romans 8.
Both based on the Cross of Christ, 2 Timothy 2:
8. Remember that Jesus Christ of the seed of David was raised from the dead according to my gospel:
9. Wherein I suffer trouble, as an evil doer, even unto bonds; but the word of God is not bound.
The one - concerning proving He is the seed of David by the resurrection from the dead - had been Prophesied.
The other - His resurrection form the dead according to Paul's gospel towards the glory of the Lord in a New Creature had been Kept Secret since the world began.
The Adversary had had not problem offering the Lord the kingdoms of this world, Matthew 4.
For he and his dark princes would still have those fallen places in the Heavenlies to traffic in their iniquity from, Ephesians. 6.
Little did he know that despite the sum his wisdom as to God's Prophesied wisdom had been, God had a hidden wisdom.
Which, had they known it, would not have crucified the Lord of this hidden wisdom's glory, 2 Corinthians 2.
Which hidden wisdom we can now know the manifold aspects of as to this New Creature by which the Son will fill all authority in all creation by - Ephesians 1:
18. The eyes of your understanding being enlightened; that ye may know what is the hope of his calling, and what the riches of the glory of his inheritance in the saints,
19. And what is the exceeding greatness of his power to us-ward who believe, according to the working of his mighty power,
20. Which he wrought in Christ, when he raised him from the dead, and set him at his own right hand in the heavenly places,
21. Far above all principality, and power, and might, and dominion, and every name that is named, not only in this world, but also in that which is to come:
22. And hath put all things under his feet, and gave him to be the head over all things to the church,
23. Which is his body, the fulness of him that filleth all in all.
Jesus Christ - "Of whom the whole family in heaven and earth is named," Ephesians 3:15.
Jesus Christ - His resurrection from the dead proving He is the Son of God; the Christ; the King of Israel over all the Earth - David's Prophesied heir, Romans 1.
Jesus Christ - He is resurrection from the dead also proving He is the Head of a New Creature far above all principalities in the Heavenlies, 2 Timothy 2.
Ephesians 3:
10. To the intent that now unto the principalities and powers in heavenly places might be known by the church the manifold wisdom of God,
11. According to the eternal purpose which he purposed in Christ Jesus our Lord:
12. In whom we have boldness and access with confidence by the faith of him.
As J.C. O'Hair had so well noted in that article on verse 10's "now" - that now is found from Paul's salvation on the road to Damascus forward...