According to a lengthy, and growing, thread on MacRumors Forums, an unknown portion of people who have updated their iPhone, iPod touch and iPad devices to iOS 9 are now complaining about sluggish performance and unexpected crashes.
Some folks are even going as far as to suggest that iOS 9 is laggier than iOS 8.
Unfortunately, I'm one of them as well.
After upgrading my iPhone 6 Plus and iPad Air to iOS 9 I couldn't help but notice overall sluggishness and considerable lag on both my devices, especially when I'm using the new task switcher or bringing up Spotlight Search.