BoxRec

15 rounds. Could Ali have beaten Patterson at this point?

Yes Ali had enough to beat Patterson in 1962.
Ali ko in 8

Cus D'Amato certainly didn't think so. In that face to face with Ali the old time trainer told him that when he fought Floyd Patterson the first time that Floyd was already on the downside with a bad back. In my view Floyd Patterson takes the decision, probably dropping Ali on his butt along the way.

This kind of thing reminds me of years ago where people made arguments that Muhammad Ali could have defeated Johansson when he was 4-0-0.

Clay sparred Ingo before the 3rd fight of the Swede against Patterson. There're different descriptions of those sparrings. Clay definitely was raw then. Patterson would edge probably.

Ali could certainly out box Floyd and use his length, even in 1962 but if he was caught by others around that time then Floyd would have caught him as well. There is no way Floyd knocks him out but he could give the inexperienced Ali more than he could handle, especially over 15 rounds. Floyds own hand and foot speed would cause Ali issues. Ali could potentially win a close UD by using his length and speed to keep Floyd on the outside but I don't think its likely.
Floyd takes a UD and probably drops Ali with a left hook at some stage.