Here's a list of phones compatible with iOS 15
The iOS 15 upgrade is compatible with the iPhone 12, iPhone 12 mini, iPhone 12 Pro, iPhone 12 Pro Max, iPhone XS, iPhone XS Max, iPhone XR, iPhone X, iPhone 8, iPhone 8 Plus, iPhone 7, iPhone 7 Plus, iPhone 6s, iPhone 6s Plus, iPhone SE, and iPhone SE Plus (2020). The update will come pre-installed on the iPhone 13, iPhone 13 Pro, iPhone 13 Pro Max, and iPhone 13 small, and it will also be available for download on the iPod touch (7th generation).