This is the better translation:
"We believe it is through the grace of our Lord Jesus that we are saved, just as they are" (Acts 15:11; NIV).
Here the Greek word translated "we are saved" is in the "aorist" tense and this defines that tense:
"The aorist tense is characterized by its emphasis on punctiliar action; that is, the concept of the verb is considered without regard for past, present, or future time. There is no direct or clear English equivalent for this tense, though it is generally rendered as a simple past tense in most translation" (The Blue Letter Bible).
So Peter uses a tense that is saying that their salvation, whenever it happens, is on the principle of grace. And since Peter makes it plain at 1 Peter 1:18-19 that these Christians have already been redeemed by the blood of the Lord Jesus it is obvious that they are already saved....
Actually, an even stronger argument is the fact that because the aorist is not bound by a time frame, it is applied when a general rule of thumb or principle, is what is being referred to.
Acts 15:8 And God, which knoweth the hearts, bare them witness, giving them the Holy Ghost, even as he did unto us; 15:9 And put no difference between us and them, purifying their hearts by faith. 15:10 Now therefore why tempt ye God, to put a yoke upon the neck of the disciples, which neither our fathers nor we were able to bear? 15:11 But we believe that through the grace of the LORD Jesus Christ we shall be saved, even as they. 15:12 Then all the multitude kept silence, and gave audience to Barnabas and Paul, declaring what miracles and wonders God had wrought among the Gentiles by them.
Thus, what Peter is doing there is reminding his own of the general principle they were already aware of - that salvation is by grace through faith.
The issue being that some were asserting that only applied to Israelites and proselytes; as only they were considered clean.
Thus, why Peter brings up the end of the difference between Jew and Gentile that he brings up there.
This "no difference" NOW as to the INDIVIDUAL salvation of EITHER, now - AFTER the Law had proven BOTH "under sin" Rom. 3:19-20, was the very principle or general rule of thumb, that Paul reminds Peter of in the following...
Galatians 2:14 But when I saw that they walked not uprightly according to the truth of the gospel, I said unto Peter before them all, If thou, being a Jew, livest after the manner of Gentiles, and not as do the Jews, why compellest thou the Gentiles to live as do the Jews? 2:15 We who are Jews by nature, and not sinners of the Gentiles, 2:16 Knowing that a man is not justified by the works of the law, but by the faith of Jesus Christ, even we have believed in Jesus Christ, that we might be justified by the faith of Christ, and not by the works of the law: for by the works of the law shall no flesh be justified. 2:17 But if, while we seek to be justified by Christ, we ourselves also are found sinners, is therefore Christ the minister of sin? God forbid. 2:18 For if I build again the things which I destroyed, I make myself a transgressor. 2:19 For I through the law am dead to the law, that I might live unto God. 2:20 I am crucified with Christ: nevertheless I live; yet not I, but Christ liveth in me: and the life which I now live in the flesh I live by the faith of the Son of God, who loved me, and gave himself for me. 2:21 I do not frustrate the grace of God: for if righteousness come by the law, then Christ is dead in vain.
Again, the aorist tense is often used when a general rule of thum is being described. Which is what the "shall be" is in the sense of, in the following passage...
15:10 Now therefore why tempt ye God, to put a yoke upon the neck of the disciples, which neither our fathers nor we were able to bear? 15:11 But we believe that through the grace of the LORD Jesus Christ we shall be saved, even as they.
The "shall be" there is not referring to a time element, anymore than it is in a passage like the following...
Acts 19:39 But if ye enquire any thing concerning other matters, it shall be determined in a lawful assembly.
It is referring to a general rule of thumb not bound by time elements like the past, the present, and the future.
Rather, it refers to a general rule of thumb; a constant that is always the rule.
Said general rule of thumb here?
The one Paul reminded Peter of in Galatians 2, that he reminds the Galatians of in...
Galatians 3:11 But that no man is justified by the law in the sight of God, it is evident: for, The just shall live by faith.