Even though some Apple fans swore it wasn't. Going to try a fresh install now to see if its any less laggy on my iPhone 6. Getting the iPad 1 form iOS 4.3 to iOS 5 vibe. Not as unusable but pretty damn annoying. Useable? Yes Does it feel like a blazing fast and modern OS on an iPhone that was just released a year ago? Nope. Seems like iOS 9 was made for the newest iPhones/iPads which is disappointing because in the past, it took about 2 cycles before devices would seen noticeable slowness.