It happens because in production mode the renderer takes longer to process everything - the render itself will be more detailed. It might not be freezing - it could just be taking a long time to load everything. Or it could be taking too long and freezing on you. I find it hard to tell the difference, sometimes :-) Neftis' hairs are a problem because of the grouping. That could be a problem with other products but none of those you've listed are known to have this issue. Turn off raytracing if you're not using it - from the image you've posted you don't have any reflections or anything so you should be able to do that without losing quality. Also if there are any objects outside the camera view, delete them from the scene: firefly loads them even if it can't "see" them, slowing down renders. Beyond that, what settings are you using, exactly? (Sorry, but I have my own defaults programmed in, I don't know what the poser defaults are any more.)