It is clear, especially with Paul, there is a strong focus on the resurrection in scripture. I think the mention of the resurrection in 1 Corinthians 15 is more focused on maturing in your understanding rather than initial salvation.
Paul does make the direct link in Romans, I think, “if you confess with your mouth Jesus is Lord and believe in your heart God raised Him from the dead, you will be saved”. That direct connection is not made in every recorded conversion, however.
I think of Cornelius who had the Spirit fall upon him before Peter finished preaching.
I think of the Ethiopian Eunuch and I don’t remember the resurrection being mentioned in that passage.
No, the mention of the resurrection in 1 Cor. 15 is not "more focused on maturing in your understanding rather than initial salvation." Paul explicitly says that the gospel by which they were saved and that he declared to them included testimony to the resurrection:
1 Corinthians 15:1 Moreover, brethren,
I declare unto you the gospel which I preached unto you, which also ye have received, and wherein ye stand; 2
By which also ye are saved, if ye keep in memory what I preached unto you, unless ye have believed in vain. 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; 4 And that he was buried,
and that he rose again the third day according to the scriptures:
Cornelius was not saved without hearing about the Resurrection--Peter preached the Resurrection plainly and even testified to his being among those who were witnesses of it:
Acts 10:38 How God anointed Jesus of Nazareth with the Holy Ghost and with power: who went about doing good, and healing all that were oppressed of the devil; for God was with him. 39 And we are witnesses of all things which he did both in the land of the Jews, and in Jerusalem; whom they slew and hanged on a tree: 40
Him God raised up the third day, and shewed him openly; 41 Not to all the people, but unto witnesses chosen before of God, even to us, who did eat and drink with him after he rose from the dead.
We do not have any basis to hold that any of the evangelistic accounts recorded in Scripture are comprehensive accounts of all that was said and took place. Concerning the Ethiopian eunuch, we are explicitly told that Philip said more than what is recorded:
Acts 8:35 Then Philip opened his mouth, and
began at the same scripture, and
preached unto him Jesus.
There is no basis in the text to hold that when Philip preached Jesus unto him, he did not testify to the Resurrection.
Testifying to the Resurrection is the very center of preaching the Gospel.