Never did this but pretty piss poor earnings for the effort and amount spent IMO. 15K Marriott probably won't get you a room in a decent area and I think collecting miles (esp 5k) is useless.
An industry standard is one room comp'ed per 10. Perhaps you can get them to comp you 4 rooms for the future or treat 4 of your guest? Wouldn't hurt to ask.
Will you get a boatload of points for the F&B & room portion of the wedding?
Best wishes.