Chapter 15 just did not follow logically or tonally from Chapter 14.
"After what happened, Madarame-san's parents learned [by some unstated method] about the situation with her cousin," at which point it somehow dawned on them that it might not have been exactly the optimal parenting strategy to go abroad for months and leave a 13-year-old girl alone in the house except for having an older teenage rapist look in on her every now and then.
(I do keep forgetting that this series is co-authored, and that wherever the writing problems come from (the editors cutting it off, or the rookie writer, etc.) Momono Moto isn't doing all the heavy lifting here.)
Sensei sure can create an identifiable tone and moody atmosphere and can put characters together in situations where sparks fly, but I think Ena from Yuunagi Marbled needs to be in every one of her stories so when the angst-o-meter reaches a certain level, as it inevitably will, she can come in and get people to act like human beings rather than erratic bundles of raw nerves and chaotic emotions.
Something would be lost, to be sure, but much gained as well.