GPU RAM size.

Apologies if posted in wrong section.

I am trying to work out the size requirements for GPU CUDA rendering for 3D software such as Blender. is there any relationship between the peak memory useage that I can see in the software and the size of the Nvidia GPU i.e. if peak memory is say 1.5 GB can I safely use a 2GB card without any crashes?

Currently using a 4GB card but looking to have a dedicated rendering tower with perhaps two cards to speed up times - often 9 hours plus. Can I replace 4GB with 2GB given the peak memory consumption.