Tired after only 15 shots? No doubt in my mind you are pulling too much peak weight. As I get older I've learned all over again that archery is supposed to be fun,, not an ordeal. I've got the weight turned back into the mid to upper 50's for my hunting bow and can literally shoot about 150 arrows each day and still am not sore the next day.

Shooting this way allows me to shoot many more arrows working on nothing but shooting form and aiming, not struggling with the bow.