Tennis ball sized groups at 15 yards is pretty darn good. You must be doing things consistently. Correctly -maybe / maybe not, you'll find out later.
I'd stick with it those arrows for now (without cutting too many more of them)) and practice practice, practice, practice, practice, and practice even more.
You'll tweak your form multiple times, multipe times, and multiple times and eventually you'll acheive a feeling in your shot cycle that's goooooood.
When your shot cycle starts feeling like second nature to you, and your bow and arrow feel like an extension of your body, you'll almost salivate when you focus on a small spot that you're about to draw on. If you're feeling this and consistently grouping tennis ball size or smaller day in/ day out - your arrows are pretty darn well matched to you and your bow. You may be able to tweak things to even better - but tennis ball groups at 15 is good to go for hunting.