First of all I always combine parts in Poseray that call the same material, so you end up with as little as possible parts. Then I always open an empty version of TG and just have the node window open, no preview. I noticed that preview on takes a bit of memory and indeed sometimes slows down working on the parts and shaders.
When all is filled in, I check with crop renders, if things need to change, I click away the preview. Works fine for me.