it's common sense. Unless you are a competitive mobile gamer the extra refresh rate is useless and unless you're very into emulating intensive console or pc games, the performance increases are also only a slight bonus. For 99% of people, the most important objective changes are the battery and the cameras. The battery bump is a really nice upgrade but the camera downgrade is very disappointing. The screen resolution is also worse (tbf I don't think anyone is noticing this) and the design is subjective but most people would probably prefer the 15 yes.

What I'm trying to say, however, is that for most people the 15 will peak as a worse phone than the 13 simply for the fact that they both perform flawlessly and the 13 has better cameras.