I have a 2010 Flagstaff Signature Ultralight and it is a really nice unit. As far as I know, Flagstaff and Rockwood are the same except for colors and branding. Mine is a Flagstaff 829RGSS and it is quite roomy for two. It's listed as "29" but it really measures out to 31ft, so I suspect the "315" might be something like 33-34ft. That is a lot of trailer, especially moving up from the PUP world. My last rig was 37ft and I'm happier with my new rig.
I will say though that except for that issue, the 8315BSS looks like a really nice floor plan. Nothing I appreciate more than a toilet area big enough to spread my elbows when the door is closed!
2010 Flagstaff 829RGSS
Still to go: AK, NL, NT, NU, YT