Why I can’t install iOS 15.7.2 in my iPhone 6s?

Hello ~ Take a look here by clicking on the following link…

If your iPhone or iPad won't update - Apple Support

What happens when you try to update ? Message? Post back with more details if the steps about are of no help.

~Katana-San~

What happens when you attempt to update?

Any error messages?

What is the existing version of iOS?

15.7.2 is only available for devices that are not capable of running ios 16.