Your hydration for that dough, not counting the oil, is only 50%. That seems very low to me. 15 minutes seems like too long to mix, but I don't know what kind of mixer you're using. In any case, overmixing will develop the gluten too much, and I've read that under hydrating also creates gluten with excessive elasticity.
I think you need more water in the dough, and you should reduce your mixing time.
Please note that I am an amateur home bread baker, and very much a novice pizza dough maker. I have no experience with commercial-sized batches of dough.