Optimize Rendering



I am new to C4D and rendering

This is my file https://www.dropbox.com/sh/4126ql4e921bpx2/AABe-R17MP831IE3YYrrS42Ca?dl=0
it takes me like 45 minutes to render on my mackbook pro per frame (6 days for the 250 frames) http://prntscr.com/gsc1dk
is there anything that i can do to make this faster without getting lower quality?

is there an option how i can make like only the background be low quality to so it should render faster?

I was also wondering why I don’t get the real colours like an actual diamond
see this https://www.jamesallen.com/engagement-rings/tension/14k-white-gold-bezel-set-pave-diamond-engagement-ring-item-53294

Thank you in advance