Can work on a full optimization of the engine?
Large interior (restaurant) in Production quality at the top-end computer produces 15.5 FPS. (32 ram, Geforce 780ti, i7 4930k)
~ 100 different light sources with shadows.
256-1024 map light.
Just for the construction of Production quality light is required at all times of the universe.
Even if you simplify the scene, then the weaker computer viewing become a turn-based strategy.
Want to UE4 replaced the Vray. Ue4 almost Vray only in real-time) + easy navigation.
An experienced programmer, analyzing UE4 said that, theoretically, if the group will work on the engine is very good mathematicians, programmers, then it can work 2-3 times faster.