Just out of curiosity, what is the total face count?

There are a number of things that can impact performance. Number of faces, modeling technique used (which can impact the number of faces to display, calculations that happen behind the scenes, etc).

Two geometries that look the same can be quite different under the hood.

But, lets start with that total faces in the model. That might tell us something. The textured diamond plate like surface - that itself could be a nightmare and have more faces that you think.

even adding fillets to areas that are important but one would never see unless you zoom in can create more calculation and faces to deal with. I am not sure how the MoI geometry kernal works, but coming from SolidWorks and other modelers like that, while working on complex models I would supress fillets and arrays where I could and then unsupress everything when I as completed with the model since I didn't care about performance anymore.