How do I fix my frozen iPhone 15?

Try a Forced Restart on the phone. Follow the instructions very carefully, as this is a bit tricky. You may need to repeat this several times.

Force restart iPhone - Apple Support

There are only 2 possible results when you perform a Forced Restart:

1) The phone returns to normal operation

Or, if the phone is still frozen......

2) There is a hardware problem with the phone that will need attention at the Apple Store (make an appointment) or take the phone to an authorized Apple Service shop.

You can find a list of authorized service shops in your area using the link just below:

Find Locations

The "Using the Community" forum is for questions about the communities themselves. You'll be more likely to get useful advice if you post in the forum specifically for your device. As you work to become familiar with the Community, you may wish to bookmark this forum site map:

Site Map - Apple Community

Regards.