I had all my snakes in 12q (same footprint as 15q) tubs until I set up a new rack recently. I had a few that were in the 500-600 gram range and one in the 800 gram range (the others were smaller). The three 500-600g snakes seemed fine in the 12q tub but the 800 gram snake seemed really cramped. Without hides (none of my bins have hides), the snake took up 2/3 of the tub and the water bowl took up the rest. He stayed on the hot side 90% of the time because he would have to move the water dish out of the way to sit on the cool side. When he did sit on the cool side the water dish had to go on the hot side and the humidity would rise (for obvious reasons). My male pastel is approaching 600g so he too will soon be in a 28q tub. I can not imagine a 1000g snake in a 15q tub with water dish and belly heat. I voted 600g.