I don't think I've every loaded that many characters in a scene, but when I couldn't render a large scene (over 150 mb file), I usually take it into Vue 4 and have less of a waiting period to render it. One thing I wish Poser had was layered scenes like in Vue. That way instead of hiding every character and piece of clothing you could hide layers and render certain parts of a scene especially when the file is large. Generally all of my Poser files are large.

Poser 2, 3, 4, 5, 6, 7, 8, 9, 10, Pro 2014, 11, 11 Pro