Hi Tom,
Since I do not have your scene here, it is difficult to tell.
Perhaps try this file
https://www.amazon.com/clouddrive/share/2Q0FeoxWg5SXsCg9DQDmL1irPB6Gqcfw9KXcM2rW7xr
Press play and check the HUD information about the FPS.
If that is not slow at all, go to the Layers and check the little icons, start with the animation (Filmstrip). You should see an enormous change.
I don’t know if in your scene is something that holds on to the data.
One option would be to play the object under a Polygon Reduction Generator. Which might take a short moment to process, but then the Level Of Detail settings can be used with this.
Besides, the XRef has an option to load a model and have a Proxy for fast redraws as one-click function.
Scene file
https://www.amazon.com/clouddrive/share/PWaBwmeSbVxxTeRwxU9yGGaL3d5WDwc8UOGFz1yG5C2
If you have a file, I’m happy to look in the morning into it. I can create for you an upload link.
For my own sanity, I use ONLY dropbox, google or Amazon as a download option.
All the best