It is now accepted by a consensus of Scholars that the verses in Chapter 14 of 1st Corinthians, saying that women should not speak in Church, are a later Interpolation.
Why then would it be impossible that Chapter 15 was added later , and not penned by Paul, or rather dictated by Paul ? It is more than likely he did have something to say on the Resurrection, but we cannot be sure that what we have in the earliest MS we have, which are 4th Century, is exactly what Paul dictated.
To be categorical that what is in 1st Corinthians 15 was written at Paul's behest is to make an assertion for which there is no proof.
Which is the problem that Bible believers have, we only have Copies of many many previous copies, we know that Interpolations, Editing, Redacting etc occurred before those Copies were made.