What's the polygon count of the ERC age? Is it efficiently modeled?
I don't know, personally, why the ERC age runs so slowly, but it runs slower than it should given the visual quality of the scene.
It needs work. I understand that - my project is running into the same sort of problem, running too slowly.
There are a lot of possible reasons for that - some of the GoW suggestions I've been given may apply here.
1) Make the geometry more efficient, reduce the polygon count.
2) Make the collision mesh simpler to make physics processing faster
3) Reduce texture filesizes
4) Minimize dynamic shadows - don't simulate shadows except where needed.
5) Use fog to obscure distant areas, or dynamic loading/unloading
6) Don't concentrate too much geometry in one view, spread it out in different areas and directions
7) Use textures to suggest more detail than actually exists in the model, with transparency maps, bump/normal maps, etc. Model only what must be modeled.
8) Level-of-detail replacement of meshes and textures. If it's far away, make it less detailed.
A lot of this is about squeezing as much as possible out of every polygon, every texture, etc.
But it looks like there's probably something more complex going on than just straightforward efficiency problems. I think the key will be figuring out what technical attribute the ERC age has that others don't.
If you can identify the difference, then maybe you can fix the problem (whatever it is that's wrong with the ERC age.)