It’s a pretty normal number for L20 for this club, I think. E.g.: それでも歩は寄せてくる ・ When will Ayumu Make his Move? ♟ - Volume 1
If people struggle it can still be changed. The thing is that nobody thinks they are ready for it until it happens and it turns out it’s completely fine.
There’s also barely a difference between it and your Option 1 - I only merged week 10+11 (which you split for some reason, despite it being the same or almost the same as week 8 and 9) and 14+15 (which is at the end, so it should be fine anyway).
(Also 15 weeks is very long.)