Will IOS 27 work on iPhone 15?

No—very likely not.

The iPhone 15 launched in 2023, and Apple usually supports iPhones with major iOS updates for several years, but not far enough to reach an iOS 27 release. On that timeline, iPhone 15 would almost certainly be past its major-update support window by then.

That said, Apple has not announced iOS 27 yet, so the exact compatibility list is not official. When iOS 27 is announced, check Apple’s device compatibility page for confirmation.