If you are going to use an open cage like yours they need places to hide. Tubs are not as open. I use a snake rack and mine have room to stretch out, a temperature gradient and water. You wouldn't keep and adult ball python in a 15qt tub. I use 41qt tubs for mine and they have plenty of room. A happy ball python is going to stay put most of the time so they don't need huge enclosures. I think your best bet is to split the cage into three separate levels. You will find it's much easier to take care of them and they will be happier. Your girl might be good a climbing, but she shouldn't be. They are ground dwellers not tree climbers.