I hope it's okay to bump this, because I want to ask about it too - when people are talking about "15-20 pages", does that mean A4 size, size 12 font?
I'm looking at my novel in A5 format, size 11 font, to try and figure out how long my chapters should be. My chapters were originally about 5-6 k each, but they seemed way too big, so I cut them all in half. But now I'm thinking of going back to about 4-5k standard size. Which seems to work out at about 15-17 pages long, in A5 size 11 font.
I'm guessing the answer will be..."it doesn't matter"?