No expert, but from reading, it seems that for the EXCs, there are race-pace service intervals and there are dual-sport intervals. If you would be mostly riding an EXC like you probably would a DR or WRR, I doubt you have to change oil every 15 hours.
If you're concerned there may be a bolt-on oil-cooler option. And with such small volume, use quality synthetic to extend intervals. It won't be DR / WRR intervals, but less frequently than the KTM manual recommends.