The release notes seem to only list the newest version that Xcode 15 support. You can download simulator SDKs back to iOS 15.0, but it doesn't seem to support < 15.0, or at least I can't figure out how to download it. You can download the available ones from the Settings/Platforms tab, + in lower left, choose iOS. Then you get a list of simulator runtimes to install. The oldest is iOS 15.0.