Secure Boot - signing FOS with your own key

The signing model — the CA/leaf split, key locations and rotation — is the same on both versions. Two things differ on 1.5: there is no --secureboot-ca-cert, so an admin-supplied key is always a flat leaf, and HTTPS and Secure Boot cannot be combined at all.

Which version am I on?

Check FOG Configuration → FOG Settings → General → FOG_VERSION in the web UI, or the version string printed at the top of installfog.sh.