Is it possible to use 'Enum' to have the local player to be r6 and everyone else r15?

No, Enum is just a constant, a value. You would need a function from Roblox that says SetPlayerModelVersion, or something like that (no such thing exists). You have to choose which model they'll end up as in the place configuration, and there's no way to modify it for individual players.

You could theoretically use Local parts to do what you asked (make everyone see their character as R6 and see everyone else's characters as R15), but it would be a lot of work with complicated scripts - I don't recommend it.