You basically answered your own question. Perc 10's contain 10 mg of oxycodone, and you stated that it takes you 3-4 7.5mg pills of oxy to feel something. If you took both percs you would only be getting 20mg of oxy, compared to the ~30 mg your tolerance can handle. So yes you would feel something most likely, but it wouldn't be enough to make you nod your brains out.