I know I will get blasted but I had a very similar problem with 2 different engines.
A TT Pro 46 and an OS 46 ax.
Bottom line, I was told by club members that 2 cycle engines do not like 15% fuel. Yes if you are lucky and dink around with the motor you may get it to work.
Say what you want but after I switched back to 10% my problems were over and both engines run like a top now.
I am not saying it will solve your problem but if you can borrow a tank of 10% fuel from a flying buddy you can test it out.