From my point of view, it seems to be a problem related to the gear. Because you're at ~815, I would suggest to do as much WQ as possible to reach ~850 then you'll see that the encounter will become much easier. It should be pretty fast to get to that ilvl. Beyond the normal difficulty, you're right in saying that you may want to start grinding AP. I will add to that; unlock your third relic, get two legendaries and do some M+ solo with each toon to gear them up a little bit more.