The creedal confession given in 1 Cor 15 has always seemed a bit off to me. It seems pretty clearly a break in topic from 1 Cor 14, but lacks the markers given elsewhere for such strong breaks (eg 7.1). The doctrinal dispute implied (There is no resurrection!) seems somewhat odd in the light of 6.14. Paul's response to food laws only works if there is agreement on that response. If there isn't agreement, we might expect Paul to have his response a little more ready; 6:14 is a long, long way from 15. 15 opens telling the Corinthians that Paul is "informing" them of something they presumably already know. Doubtless Paul has already "informed" them, and even without speculation of what Paul's preaching consisted of, we can safely assert that he "informed" them based on 6.14 (on the difficulty of the verb here see TDNT 1:718, the difficulty is substantially resolved here if Paul didn't write it). Perhaps most importantly, it describes Paul's "gospel" as almost an exclusively past event. Which is markedly different from the more generally Pauline use of it as a present reality that extends into the future.
While commentators have noticed all of these irregularities, of course (I'm but a dilettante, you don't think I'm coming up with these on my own, do you?!), there hasn't been any real inquiry (as near as I can find) into the possibility that 1Cor 15 isn't authentic. While the possibility has been raised that it represents a different letter, I'm unaware of any serious look at the possibility that it is not Pauline. Robert Price wrote a brief piece on the possibility, but it is rather standard Price fare--lofty rhetoric, but no clothes on the emperor, it's a look, but calling it a "serious" look is probably more generous than we should be. The piece might raise an eyebrow, it's unlikely to win many converts.
I'd venture the reason for this is two-fold: Firstly, largely by necessity there is a general reluctance to question the manuscript evidence in the case of the Paulines. We have to start with the assumption that the manuscripts are telling us the truth. The burden, of course, rests on the one claiming interpolation, and it is a lofty burden to bear.
The second reason is that it provides such a nice, convenient definition of what it was to be a member of the burgeoning Christian movement. We can handily point to it and declare that an early Christian is someone who believes that, for, "I or they, so do we preach, and so have you believed."
So, with the culmination of my five brief points on Doherty's book tomorrow or the next day, I think it might be an interesting exercise to see where the evidence takes us if we look seriously at the possibility. I'm suspicious of the passage, but not convinced in either direction, so my conclusion may well surprise myself more than anyone else.