I just went back to check for you on our fleet of 2015's and they Do!
The 2015 Mustangs do in fact have collapsible mirrors.
Are you planning on picking up an S550 for yourself?
Hahaha no I'm not planning to buy a S550
I have my 2013 GT only since three months
But I really like the new one with all the new features. But I think I love my mustang too much to sell it