Well i have never used a 15qt tub. We keep our hatchlings in a 6.5 qt tub until they reach about 400-500 grams then we bump them up to a 28qt tub. The bigger females are in a 32qt tub. We build all our racks so far so we keep the variance of tubs down to a minimum. You probably can keep a 1000 gram snake in a 15qt. Hope this helps.