I updated to 15.1. and everything seems to be working great so far, except for:
I noticed that my calendar won’t sync anymore (no error message, just nothing happening)
So I reinstalled Davdroid (also tried earlier versions) and now my contacts and calendar apps can’t find my davdroid account anymore, so all entries are basically gone.
The davdroid account appears in the system accounts list, but the apps can’t find it / can’t connect. Davdroid itself seems to be working fine.