It should be at least 14. I think it is possible to miss the 1 point by not exposing yourself to Lucy in the bath, and I think it is possible to do Rachel in such a way that Sex Ed class and the girls locker scene do not trigger right away, but of the other possible, you should have 14.
In Chapter 1, you get 1 each from punishing Amy in class, Liz' blue underwear, first version of putting sunscreen on Liz and Faye, The TV show, and watching Secretary on movie night, and then 3 for completing the chapter (and 1 from Lucy's bath scene, which can get skipped).
In Chapter 2, you get 2 from Cassandra's paddling and group scene, and one each from Liz' classroom punishment, second version of sunscreen for Liz and Faye, CPR class when opening pool, and Emily gossiping about your schlong (and 2 from locker scene and 1 from Sex Ed, which can get delayed).
That's 14 that I am not sure can be avoided while still completing the related quests. Any idea which one you didn't get?