That you are breaking core functionality like calendar, contacts and tasks with a release and don’t think something is wrong with that, is bad enough. You should have withdraw the 15.x upgrade.
(Anyway, when will these functions be available again?)
But my main question is: how can I qickly downgrade to 14.x?
(I’m pissed; really, really pissed and considering throwing money at apples face for that proprietary icloud solution… grrrr)