Don't know specifically if it will fit (never shop for wide boards personally), but if that's the widest you can find in a board you want, there are a couple of things you can do to make it work better.
Change your binding angles. If you ride duck, the wider your angles are, the narrower your boot profile will be on the board. If you ride a forward stance, make your angles more forward much like an alpine snowboarder. This will also reduce your boot profile, might make freeriding/carving easier, but will make switch/park riding more challenging.
Widen your stance. The listed waist measurement is generally at the middle of the board, but virtually all snowboards taper to the middle and are thus wider as you move outwards. A wider stance generally puts your feet at a wider section of the board.
Do either of those things ONLY to the point that you are comfortable. You should never have to dramatically change your stance or angles just to fit a snowboard, but I guess with size 15 feet, you make do with what you can.
I would contact a few reputable board shops and get some expert advice, with hoofs like that you really need the widest board you can find and those guys do it day in day out so they will be able to make you some good recommendations.