I believe Bryster is one the right track. 

I had a similar experience when i made the Masters Series scene "The Block", where one single material brought the entire system down on its knees. Once i replaced that material, the scene rendered in less than 30 minutes, highres.

In my experience, Bryce normally don´t have much issues with massive scenes and highres textures as long as you use booleans and/or terrain objects. In fact, Bryce normally handle large scenes with 2-3000 pixel resolution textures better than most of the professional apps combined. :)
However, imported meshes is not always running as smoothly, and often those in combination with one particular texture can cause memory issues.

This may not be the easiest solution, but if i were you, i´ld grey the scene, and reload each texture to pinpoint the one possibly causing the issue. 

Rudolf Herczog
Digital Artist
www.rochr.com