(First I now better tell a little secret that I kept for quite a while already, in case someone was wondering: As you can see in my sig or may remember I pre-ordered an A16 in June 2017. And I am still waiting for that one. But I bought another A16 from a kickstarter backer who already received it. Practically unused, 16 channel headstand version.)
In each listening room, in submenu 'Configure' there is a setting 'HT offset'.
As you now know I have a 16 channel A16 in my possession. After upgrading from 2.11 to 2.12 I also had "rotated" speakers.
Then I checked the "HT offset" setting. In all listening rooms (4 x 32 = 128 listening rooms
) it was set to '10' (meaning the speakers are rotated 10 degrees relative to position of the headtracker).
So maybe something similar could have happened in your case. After upgrading check the 'HT offset' setting. (And first check what it is now.)
Although I would find it strange in a few ways. Why with 2.15 in your case, and 2.12 in my case? Why would it be back to 0 when you went back to 2.12?
By the way: I did not upgrade to 2.15 yet.
[Edit: I changed my signature accordingly.]