I did download the ios 15.5 every time i try to install it on my 6s iphone it is not verified and am not able to install it

So, you turned off Low Power Mode and connected to a stable wi-fi network and it wouldn't work? If not, then see this. If you can't update or restore your iPhone or iPod touch - Apple Support and also this. If your iPhone, iPad, or iPod touch won't update - Apple Support

Between the two of them you should get it to work. If you get a different error, come back.

And Low Power Mode needs to be turned off.

Ahmed_sherif7 wrote:

https://discussions.apple.com/content/attachment/7be60591-2301-4e83-9683-5322a4ae567c

Your phone needs to be connected to wifi.