Question Caching a scene

Hi
I have one large scene with lots of 3d graphics etc that takes a few seconds to load. Sometimes the user will switch to much smaller scenes for specific tasks e.g. form entry. I have one scene that demands it sits independently from a 3rd party developer. The other scenes are either small 2d scenes and 1 3d videoplayer.

The large scene is where 80% of time is spent. Therefore I would like to keep it in memory as I swap to the other smaller scenes, so it loads faster when I return to it.

How would I do that? I have searched for scene caching but not found anything applicable.