How to install iOS 15

Hello ~ Take a look here by clicking on below…

Update your iPhone or iPad - Apple Support

If you can’t update…

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

Work through the link and post back if needed. The last link offers some common issues that may prevent updating.

~Katana-San~

To update your iPhone 6s, select Settings > General > Software Update. If your phone is eligible for an update, you will be prompted to do so. This link offers more information.

Update your iPhone or iPad - Apple Support