That's tragic to say that Paul was merely summarizing in 1 Cor 15. To essentially accuse him of having left out one element of salvation, that's a level of slaughter that I'm not willing to traverse. I've heard that kind of reasoning from Mormons and Jehovahs Witnesses.
No thanks. That's strictly on you. If water baptism unto remission of sins preached to Israel by Peter were still a requirement under grace, then there is no grace, but only works.
Good luck with that. You're going to need it.
MM
Read Acts13 and later and realize Paul's history in Corinth teaching for 3.5 years. He begins 1Cor15 referring them back to the Good News he had taught them. In Acts13 he had proclaimed Christ's death, burial and resurrection within a more comprehensive Gospel to Jews and God-fearing Gentiles, wherein he also referenced Ps2 to tie Jesus into being YHWH's Christ & King.