Why does complex material take too long to be rendered?

[fa2020]

Hi,
Recently I downloaded a ring model from GrabCad and tried to render it using Keyshot. I applied one of complex material which I'd downloaded from the cloud. The material contained some procedural maps that one of them was curvature map.
After all when I tried to render it, it took too long to remove all the noises. after about an hour noises existed yet. Finally, I dismissed the render and turned off the PC.
I should mention that my scene had DOF effect too.
Why is KS too slow in complex materials?
my render resolution was 1600*1200 that is not a large image.
my system specification is:
CPU: Intel Corei7 4790K  4.0 GHZ
RAM: 16 GB DDR3
GPU: Asus Radeon 290 3GB VRAM

[Esben Oxholm]

Complex materials takes longer to render because they are more complex

More details about what specific material it is would be helpful check out why that particular material is heavy.