Why i cannot update ios 15 to my iphone 6s

If it's telling you you're running 12.5.5 and that's current, you do NOT have a 6s. You have a 6 or a 6 Plus.

Thank you for your reply!

See>>>If your iPhone, iPad, or iPod touch won't update - Apple Support

fairuz86 wrote:

I cannot update ios 15 to my iPhone 6s

Go to Settings > General > software update > what do you see ?

what is the error message that you see when you try to update?