I know 15 gallon seems a bit excessive, however they are all 3 reveged from being budded out in 5 gallon pots and I read everywhere and it was my understanding that when doing a reveg you must bump up pot size, also they would get root bound fairly quick I would imagine. Once I get them going really well and am pulling off some good cuts I will grow out the cuts into moms so I don't have to keep them in such big pots......I hope this makes sense, one of those things where I was unable to take cuts prior to flower and want to keep the strain alive, it was incredible