Yeah, it seems that the game will have 20 chapters for sure.
It's possible to still wrap this game up in 16 chapters, but I think it would feel pretty rushed in that case. We have at least one more round of Ian's MMA tournament (though I'm still hoping for two), Holly's book release / announcement of her third book, Lena's music competition, Ian's book release, the mayoral election, the living arrangement shake up. And I'm sure I'm probably forgetting another Seymour plot-point in there too.
The two book related events and Lena's music event could make for a single chapter, with a few other side character plots wrapped up. Then Ian's MMA and the mayoral election could be the other chapter and that puts us right at 16 chapters (assuming I'm not forgetting some other significant event). Then the epilogues can resolve the living situation for all of our characters. Again, this will feel pretty rushed, but it's possible if not plausible. Especially since it's a safe assumption that something else is going to come out of Billy's event for Lena, Ivy, and / or Jeremy.