I’ve had for just over four years an iMac late 2015 Retina 27" i5, Radeon R9 M395 2GB, main memory 24GB with a Fusion drive.
That’s arguably a slightly better spec than your machine - faster single thread CPU GHz, but i5 vs i7. It bogs down on a HUGE model I’ve helped to develop - 800MB and still heading bigger, but works reasonably well on a part of that model.
The sub model is ~300MB. 27 million edges, and over half a million component instances, loads in under 2 min, and with about half of its MANY layers/tags (too many to count accurately, but at least several hundred) turned off, is quite speedy in response to orbiting, zooming, and editing.
If you have Outliner or Component Browser windows open it slows down drastically, and the load time goes WAY up.
The original developer has a more powerful i7 processor and he can handle the full model in both SU and Layout. I’ve never needed to try it in Layout.
There’s a fairly recent thread on the forum comparing different configurations of Mac and Windows machines on a test SU model. See where yours comes in comparison.
My impression is that performance on the test SU model in that thread doesn’t vary all that much between different spec machines - less than a factor of two between fastest and slowest IIRC.
For reference, my machine on that benchmark came out at
72 frames displayed in 3.0880 seconds
Average frame = 0.0423 seconds
23.6395 frames/second
My own and my co-modeller’s impression is that there’s a point at which the growth of the model slows down performance fairly suddenly. Managing layers in SU seems to be the key. Turn off all layers with heavy geometry that you don’t actually need while modelling. Make sure you don’t overload the model with over detailed high poly models from the 3D Warehouse. Use images where possible instead of heavy SU geometry.
So improved hardware will help, but not dramatically, in my view. Attention to efficient modelling will pay greater dividends. But if you are already doing that. a faster single thread performance and perhaps a higher spec graphics card will heip but not magically solve slow performance.