I have a 6. My instincts tell me to leave it on IOS9 and that 10 will choke my phone pretty badly. For those that have tested 10....opinions?
I wouldn't worry - I sold my 6s and using my old 5 for a few weeks in the meantime, and it has had the public beta of 10 and it runs as fast as it did on iOS9, so i dont imagine the 6 will struggle..