15.4 is, but I think your command there shows the version of xcode-select itself.
I don't have a Mac at hand atm, but this is what the CI does:
Code:
sudo xcode-select -s /Applications/Xcode_15.4.app
xcodebuild -version
xcode-select -p
xcodebuild -version shows the version, xcode-select -p shows the path, and sudo xcode-select -s is to set a different one.