Zone load-in (especially Hew's Bane) was awful up until the last patch. I constantly experienced triple load screens in cities, environment not drawing in, etc. Since the last patch that has all gotten better, but now my fps during dungeons is dropping to zero. I'm running a Sorc with lighting and once we start the fight my frame rate locks up constantly and just drops to zero or 1.
I'm sure you get 100 of these per day, but I just putting it out there. The game is not breaking any ground in graphics and PS4 hardware is sufficient to run a game like this in 1080p. I'm not in Cyrodil with 500 people running around, I'm in a 4-person dungeon.
I also play The Division on the PS4, and the graphics are far beyond anything ESO renders, and I have no fps issues at all in those 4-person missions.
You've got to optimize your game.
I've got 30Mbps down / 5Mbps up. It's not my internet connection.