I have no doubt that there are many 15 year olds (and younger) than can properly care for a ball python or even several. And the OP seems to have a good idea of what they need for their ball python but when it comes down to it, it doesn't matter how ready YOU are. If you parents are not ready for the responsibility (and trust me, it will be partly their responsibility too. It is living under their roof, sudden vet bills, electricity, etc), then the answer will be no and you should respect their decision.