Hi Ehmie,
If you place Polygon objects on Layers, you need to shut off more than the visibility. Typically the solo option should help a lot, if you use many Layers and solo only one.
My tip, go to the Editor View>>Option>Configure All>>Attribute manager>HUD>Frames Per Second (enable). this gives you a Screen redraw, frames per second. The Lower it gets, the more the machine has to work. In that option you can also check on the HUD> Open GL Statistics, to check what is currently working inside your scene.
Now you can check what really kills your performance.
Dependent on what area you machine has the bottle neck, it might help to even switch textures off.
As you work already in Polygon mode, the main tip is of course to check if your models are optimal, in other words have too much points and edges with no quality improvement.
Is the City Build with MoGraph,—switch parts off. Even polygon models, which are in some way newly generated, will lower the performance.
Perhaps separate what is only during rendering needed, and link it to XREF. So you can easily switch that off.
Normally there is more, but as you mentioned, it is about polygon objects, I hope to have given you already some tips.
In the way you have set up your preview will also influence your scene.
In the Editor View>Display, you might find some settings that lowers the performance as well. I’m not certain how much Back-Face Culling will help here, make tests.
All the best