When setting up scenes like this, I usually switch to Sreed preview and any of the display styles but texture shaded.
Then I prepare every figure in it's own scene.
Loading figure, hair, clothes, materials... pose figure... save as .pz3
I do that for every figure, that's supposed to be in the scene.
Finally, I open my future final scene and import all those pz3 one after another and all I have to
do is move the figure to it's place....
That way you don't have to wait for ages when loading items, applying and adjusting poses, etc.

Finally, before I start the final render of such a scene, I restart Poser to clear all caches.

All in all, you can work much faster when building up your scene and you don't run into any out of memory errors.

Yesterday's the past, tomorrow's the future, but today is a gift. That's why it's called the present.