Good day bro. What you have computed is the probability that all of my 15 dratinis won't have H.A.
If you want to tell me what is the probability that atleast one of those 15 will have H.A., you must treat every dratini as exclusive events. Search more about probability and statistics so that you wont confuse others. Thats what i always tell my statistics class.
Anyways, thank you for entertaining my concerns. I guess i just have the worst luck today. Have fun playing