I believe that you are on the right track, John. I took a look at the file and that strikes me as a place to start optimizing the shape.
1. I have never found MA3D to handle texture bitmaps applied to shapes well, this is where it chugs. To that end I use no bitmap textures when creating shapes/models for MA3D. I also use as few Materials as possible, which substitute as Bitmaps just fine, the only exception would be some sort of Alpha related transparency for a special effect or visualization. Not really needed for working the lights in the software...in the Stage View. Rendering out for promotional reasons or client cultivation, sure, art it up...
2. A very fine model, brother, my compliments! I did notice quite a bit of detail that, again, is not really needed when representing the fixtures in a 'working' situation, which you are experiencing at the moment. The bolt holes in the dimmer connector panel brackets in the grid generate a TON of extra faces that are chewing away at your system...these minute details, which will never be seen by the end user, are what can cause a bottleneck in the render pipeline.
I think your performance will definitely improve if you go back over the Scene and eliminate the UV mapping to the all of the shapes that have it, not really needed if you are just applying a simple color/diffuse Material for the visualization. If you want to keep the mesh/alpha .JPG...go ahead, I only saw the single bitmap embedded in the Scene, but be prepared to shed that from the environment if things still chug.
I'm gonna try a few things here, lot's of 'free time' on my hands, ahem, to see how small I could get a good representation of the venue for programming. Again, a great looking model!
Good luck!
PS: the soft goods as well can be causing rendering issues, with the many actual 3 dimensional folds you've included...they could in be visualized as flat panels the actual width, all those shadows, sure look nice, but bogs things down in the 3D Views...
PPS: here's a quick and very dirty optimised file back...all UV's removed, will kill your .JPG textured object's visualization but the file is now 1/2 the size it was...give it a try/evaluation. There is more that probably could be done, more mesh group/material optimizing...like grouping all similar shape[all the hang pipes, etc] using a similar material, these types of steps really do help by keeping things simple for the systems to digest...I even 'crunched' the vertices from over 200,000 down to like 30K...I think that MA3D does some 'unwelding' when reading the 3DS shapes/groups, as the size tends to bloat once Imported into the system and inspected.