I'm running a Threadripper 2950x with a GTX 1080 Ti.

I've got about 150k verts in a very simple scene (9000 teapots, just testing something basic out) and the viewport is rendering at 10fps flat shaded. Wireframe mode drops this down to 3-5fps!

What could be causing that?

I've posted the file in case it's something obvious.

EDIT:
After converting to poly it seems to have improved it , are they NURBs? Is it just business as usual for NURBs to be that slow?

Regardless, I'm still getting roughly half performance when switching to wireframe mode.

There's a lot more GL primitives to draw when ghost wireframe is active, especially ghost wireframe as it draws the shaded portion to mask out ghost lines, then the wires themselves. NURBs surfaces are also drawn as separate batches, so in the flat shaded case you're getting 9000 draw calls, and wireframe ghost is 18k. In the case of the hip file you provided, they're all unique GL primitives, not instances.

The best thing you could do would be to enable “Pack Geometry before Copying” (Stamp tab) so it instances. Then you're only affecting the transform on a per copy basis, not the nurbs itself. This reduces the draw time to 7ms for me. This is because now there's only 2 draw batches instanced 9000x, which the GPU is much happier with.

Ah I see, that makes sense. Rookie error on my part then!
Thanks for the help