To answer the question: Runey has mentioned that, based on his current knowledge, Ren'py has a size limit of 2 GBs for .apk files. The game, as of update 0.18.2, is ~12 GBs in size. Another method will be required in order to create an .apk file for the game.
I vaguely recall someone suggesting a method, but I could be wrong about that one (it's been awhile). But to reiterate: the .apk file can't be created by itself due to the size of the game.