I can't do the 15 minute thing, I just hit my stride and have to stop, so I do 30 minutes of the decluttering. The key is never leave the room you are in until the time is up.
My main tip is start at the door and work clockwise around the edges of the room first then do the center.
Also I add a 3rd box/bag. Things to give away or take to Goodwill. That one is also critical in my projects as most of what doesn't belong there is stuff we don't really need at all but is too good to throw away.
Oogie McGuire - Mac, iPhone & Omnifocus
OogieM on Twitter
Paonia, CO USA