If anyone is thinking of updating to 5.15.9, I wouldn't at present, 5.15.8 seems to be ok.
There are quite a few packages that are failing to build, or corrupting applications already built when run with this version. Most have stepped back.
There are over 30 individual packages found affected so far.
I sugest you await till either the next version comes out or a general set of fixes appears.
UPDATE1 :Apparently this has been caused unfortunately by a regression in Qt's CMake translation API. A buglet (report) has been already submitted to them.