In the Samplings settings box under Render I tried the Samples setting at 12, 24, 32 and 64
12 = 144 Samples
24 = 576 Samples
48 = 2304 Samples
64 = 4096 Samples
Ray tracing is expensive, but the interplay of light with the scene might be worth it. I love how the blue coffin light reflects off the robots back and illuminates the back of the scene as he moves toward the camera. The realistic soft shadows are hard to argue with also.