I am in the same process of building a new 2-channel system from scratch and am just about done.
I have the McCormack DNA-500 (uh, also for sale on a'gon btw) with the smallish Merlin TSM-MX monitors in a relatively small space (13x18x8). The press on these is definitely NOT hype. This amp certainly doesn't exhibit it's power reserves in a negative way like most behemoths. It is actually the best sounding of his various offerings, including the heavily modified ones (by Steve Mc). It has a great deal of finesse and is very smooth sounding overall (sort of like a good tube amp, but not colored at all). If it wasn't for a certain set of tube amps, this would probably be my keeper. That said, there are many alternatives suggested available here like the CI D-200, NuForce 9, Odyssey Stratos which would fit the bill. I'd also pay close attention to the interconnect, speaker cable, power cord, and power conditioner budget as these may eat it up pretty fast and do make a difference in overall setup. Again, many good ones on this site (Reality Cables, Bolder, Ridge Street Audio, etc.).
For speakers I have the Odyssey Nightingales ($1295) and both small and larger Merlins (TSM-MX and VSM-MX). The Merlins are certainly in another league both price and sound wise, but either one should be on the audition list. A used set of TSM monitors supplemented by a REL sub would be both very satisfying and economical in a smaller room. They are usually available on a'gon, but watch which version as there are many upgrades available from them (call Bobby P at Merlin FIRST). This combo would be hard to touch without spending a lot more money. The Odyssey Lorelei's may be one of the best speaker values in audio, though they may be hard to place with a rear port in that 15x15 room. You don't find them on resale for good reason, but even at list they are very reasonable ($2795). You might give Klaus a call. Jim Salk's HT3's are also popular in this site. The ones I've heard sounded great, but you'll have to wait awhile for him to build them (though clearly worth it). Again, no resales out there on these.
The other comments on here about room treatment are spot on. This will likely be your biggest challenge so take a look at the many products out there and seek advice from some of the expertise here and save some of that budget for that battle. My inclination is to get the best components I can afford, then start dialing in what I need in terms of room countermeasures gradually. If you're really in trouble, pieces like the Tact can really tame a misbehaving room quickly.
Good luck in the hunt!