It definitely can be doable. 15 + bride and groom is pushing it IMO. I think they say the boat holds 18 but really if you expect people to be in the lounge area at one time (for a meal or cake cutting) it will be really tight. That number is if people are up on the top, in some of the rooms, and out on deck. We celebrated our dating anniversary on the Grand One and it was just the two of us but I want to say maybe 6/7 adults would fit in the lounge comfortably. How about using it after your reception for desserts and fireworks?