I'm not sure if you're familiar with the ingredients in Percocet. Percocet is a combo of Acetominophen (Tylenol) and Oxycodone. You said you're taking 10/325 which is (10mg Oxycodone) and (325mg Tylenol). Have you been being given the brand name "Percocet"?
If so that's a shame, because the brand name is more expensive for no other reason than "the name". Your doc should know this. Your pharmacist should also know this.
Anyway, the Oxycodone #15 (15mg's correct?) will be very effective, and since you've been on this med for so long, it will be much better to give your liver a break. (Tylenol is very toxic to the liver). The max amount per day for Tylenol is 3 grams or (3000mgs.) same thing.
Watch the Oxy though. That is some of the most addictive pain med out there. Compared even to Hydrocodone (Vicodin).
Hope this helps