No security check DOM-INT at OSL
If your luggage has been checked through (or you travel only with hand luggage as you do) you do not have to go through security at OSL. If you are on a through itinerary, you'll probably get your boarding pass at TOS, if not carry a written proof of your itinerary, and you'll get a boarding pass at the gate (the confirmation or boarding pass necessary to get trough the manned door to INT, and through passport control to the non-Schengen gates).
No wait at the entrance to the INT part of the terminal, usually just a short wait at passport control. As there are few facilities past passport control (just a small newsstand and cafe), you're probably better off waiting in one of the bars/ restaurants in the INT terminal or in a lounge if entitled. The lounges are all in the Schengen part of the terminal, i.e. pre-passport control.
80 minutes is about double minimum connection time at OSL, but not over-long as the non-Schengen gates are at the far end of the international terminal. OSL is LONG, about 800 meters, so count on a 10 - 15 minutes walk from arrival gate, to LHR gate. Arriving DOM passengers might have to backtrack from the arrival gate to the stairs to departure level.
In my opinion, connecting often at OSL, your connecting time is comfortable.
But as I started: no security check DOM-INT at OSL or DOM-DOM. Just for INT-DOM and INT-INT