What gospel did Paul preach in Corinth?

Paul preached the gospel that Christ died for our sins according to the Scriptures, was buried, and rose again according to the Scriptures. That was the only gospel Paul knew; out of it came multitudes of pagans, and he turned the Roman Empire upside down.

Les explains that Corinth was a bustling double seaport and commercial city, surrounded by abject idolatry and paganism, with a large Jewish community. Into that ungodly city Paul came with no fanfare and no advance men, and he simply began preaching the gospel. Les points to chapter 15: Christ died for our sins according to the Scriptures, was buried, and rose again according to the Scriptures. That was the only gospel Paul knew. Les notes that out of that preaching came multitudes of pagans, and Paul literally turned the Roman Empire upside down. To Corinthians plagued with temptations, problems, and testings, he later says in verse 13 that no testing has taken them but such as is common to man.

1 Corinthians 15:3

For I delivered unto you first of all that which I also received, how that Christ died for our sins according to the scriptures;

1 Corinthians 15:4

And that he was buried, and that he rose again the third day according to the scriptures:

What does Paul mean when he calls the gospel 'my Gospel' in 1 Corinthians 15?

Paul calls the gospel 'my Gospel' because it is the message he received and preached: that Christ died for our sins according to the Scriptures, was buried, and rose again the third day according to the Scriptures. This is the gospel he identifies as his own in 1 Corinthians 15.