are you sure it's going to trigger if you start below 15 and pick up the two +1 vice options to wind up with 15 or more before the last decision? i notice that vice before and after that event actually doesn't change for me regardless of choices, so it seems that those options might not be updating vice properly
if that isn't it let me know and i can upload a save but that seems to be the cause of the issue for me since i'm aiming to go in with 14, pick up +1 vice twice from the two choices and then have 16 for the third option, but after the event ends i'll still have only 14
edit - actually, the issue is more general: vice is not actually updating past 14 at all, including decisions from e.g. blackmailing the alchemist