Assuming the VRay renderer is GPU based, you'll need a compatible video card with VRAM suitable for the scene you are attempting to render.  You can improve performance almost linearly with multiple parallel cards *but* you'll never get a 3 hour => 3 minute reduction on a desktop.  Even a render farm might not get that kind of performance increase.  And, of course, hardware is only part of the equation - properly optimized scenes are also necessary for faster renders.

Anything that can handle high-end rendering will handle 2D AutoCAD, so I recommend you take this to a VRay forum for more complete answers.

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If you are going to fly by the seat of your pants, expect friction burns.
"I don't know" is the beginning of knowledge, not the end.