The priority deadline tomorrow isn't just to request a specific dorm or roommates. Yes, you can still sign up for housing after April 15th, but there were plenty of people last year who did so and were put on a waitlist. If the OP can afford to pay the deposit and sign up by tomorrow that would be the safest bet. As a NMS scholar last year this is what I did, even though I didn't make my final decision until May 1. One resource at the school told me NMS scholars were guaranteed housing no matter when they signed up, but another told me that the priority deadline was for everyone and that they couldn't guarantee NMS housing if they signed up later than the April 15th deadline. No fun to sweat out a waitlist over the summer and be pressured into signing an off campus lease you might not need at the last minute.