I'm not the best to give personal experience on this, I don't have any vision tubs. But I have looked at them a lot and seen what a lot of people had said. The v15's I haven't looked into much, but that's because everyone uses v18's for hatchlings just fine. But I've seen people say they keep snakes up to like 800g with 500-600g being the typical point where they move them up. The v35s are basically 28qt sterilite size (close enough) so I'd move everything from the v18 to the v35s at 500-600g and then when females get to breeding weight I'd move them up to a bigger container (41qt sterilite or cb70).

This link gives you a good example of what size snakes look like in the v18 http://www.metalmonkeyexotics.com/blog/?p=4643