But there are two of Yoyogames's games which are beyond this 15MB limit
Doesn't bother me as me and my team are doing everything we can to cram an RPG into this limit but others may want this question answered.
It isn't a hard, or fast rule, the doc is simply about designing iphone games. You want mobile games to load, and run quickly.
To speculate, I assume the GM iOS runner, or code base is quite large. Prison Ball, which is a 2mb-ish file on the PC, (most of which was the GM-runner, anyway). It hits 37 mb on the iPhone, although graphics were re-vamped during the port. Granted, that was in the 'early' days of YYG's porting stages, I imagine (and it would seem) that the file sizes are getting smaller. Also, it incorportes things like game-center, etc, which I have no idea how large they are.
But yeah, I'd assume that GM will run at least 10mb onto your game file, at least, until told otherwise.