I remember one time my project froze when turning the camera in a certain direction on a certain level. I couldn’t think of anything smarter than to remove 50% of the actors from the level to find out which of them was causing the freeze. Then another 50%, and another… And so I found out that the problem was in the volumetric fog in the background, which in general does not affect the picture in any way.
And the funniest thing is that it was a default actor from a template level, but at one point he started to ruin everything. 
I think you can do it in about 30 minutes.