If I ran into a 15+ multiboxer in PvP, I would thank them for their donation of 15xsubscription to the game.
You should have the focus somewhere else, as any good cheater with AI today, can basically run the game better than you can. Already heard about people training ai on private servers to use. Better to find the solution in other ways, basically making them less useful, because that would allow for adjustment behind the scenes, that you just cant mimic and take into account.
Trying to ban them, just hits some small fish and legitimate users.