Any disc brake that will fit inside your 15" wheels will have marginal performance at best, and it's probably going to be impossible to find 8-lug discs that small. The split rims will help a little, because they won't have the drop centers necessary to mount tubeless tires.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!