Update my phone
yes
iPhone 6s, iOS 15
Question marked as
An iPhone 6S can be updated to iOS 15.7.9, no further.
Go to Settings > General > Software Update.
This link will show you how to update your iPhone, iPad, or iPod touch using WiFi -
Update your iPhone or iPad - Apple Support
This link will show you how to update using your computer -
Update iOS on iPhone - Apple Support