The iPhone 6S was released on the 25 September 2015^[1], which marks the beginning of its update period. On the 12 September 2022, the iOS 16 was released, a next version of the operating system, which not made available for the iPhone 6S, thus leaving iPhone 6S on the the previous version of the operating system, the iOS 15^[2]. This date marks the end of what we consider its update lifetime.

These two dates are 6 full years and 0 full months apart, which gives it S- tier.