iPhone 6s update

An iPhone 6s, iPhone 6s Plus, iPhone 7, iPhone 7 Plus, or iPhone SE 1 isn't capable of 16 or above; they require an A11 or better CPU.

(254155)

No, it cannot. That iPhone does not have the hardware to update any higher than 15.8.

Nope, iOS 15.8.2 is the limit for what the hardware on an iPhone 6s is capable of running.