I would not be surprised if it was related to ACIS History. One indicator is if TurboCAD will eventually display everything, but takes a long time (another is having a design file that is in the tens of megabytes).
As an example, I recently created a docking platform prototype for a MacBook Pro laptop. To get that diamond pattern in the frame, I had to 3D Add dozens of Boxes to create the basic pattern, then I had to 3D Intersect with another solid that specified the boundaries of the main section, followed by a 3D Add of a Shell of that same boundary to get solid faces on the bottom and sides.
It literally took upwards of 5 minutes to do a Draft Render (maybe more... I got bored and did something else while I waited).
When it finally occurred to me to check the ACIS History, I Exploded all the components into ACIS Solids.
Rendering now takes about 2 seconds (IMSI should really update the ACIS History code to Multi-Threading).
To see if this is what is happening to you, bring up the Selection Info panel (the fastest way is the <Ctrl> <Shift> I hot key) and start clicking on objects (you may have to make all hidden Layers visible as there are a couple bugs relating to this).
Or it could just be the file size. This same MBP Cradle does take a long time just to load to Wireframe display because it's 42 MB.
TC Pro Platinum 2018, 2017, 2016 & 2015 (all with LightWorks & RedSDK) & V21
System: i7-5820K @ 3.30GHz, ASRock X99 Extreme4, 16GB DDR4-2133 RAM, Gigabyte GTX 970, Samsung NVMe SSD 950 (256GB), Windows 7 Pro (64-bit) SP1