You need to look again for understanding, it is to the elect, which includes the entire body of which there is only one.
And this, showing we are also included:
"And count the patience of our Lord as salvation, just as our beloved brother Paul also wrote to you according to the wisdom given him, " 2 Peter 3:15.
Just as Paul's epistles were written to and were for both Jew and Gentile, so too Peters epistles. You're merely twisting Scripture as Peter solemnly warned against in the next verse and context.
Paul preached Christ to Jew and Gentile from the law and the prophets as well as the mystery (Romans 16:25-26); there is nothing to indicate Peter wrote to Gentiles that I know of.
Peter acknowledged that Gentiles believed his preaching in Acts 15:7, but the gospel they responded to was the gospel of the kingdom, not the gospel of grace. These Gentiles are talked about by Paul in Romans 9:24-31. These Gentiles were part of the believing remnant of Israel.
Peter was speaking of the coming of Christ and longsuffering.
2 Peter 3:9 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.
2 Peter 3:15 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;
Paul spoke to Jews as well in his epistles, Romans 7:1 for example. In Romans 2 Israel is dealt with, and below, in Romans 2:4, he speaks of longsuffering. This is the kind of writings Peter is talking about in 2 Peter 3:15.
Romans 2:4 Or despisest thou the riches of his goodness and forbearance and
longsuffering; not knowing that the goodness of God leadeth thee to repentance?
2 Peter 3:16 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.