Okay, thanks for all the suggestions! Here are some observations.
All my models are wrml, I use the export feature from FreeCad, it seems to work very nicely, even the colors are correct.
What I mean by render is the first time I click on 3D View, or if I click on any of the tabs in 3D View (Setup, Preferences etc.). Once the board is visible, I can rotate it, zoom in or out just fine. If anything has to be regenerated I get the spinning wit wheel…
Blank board- it is very fast, less than a second to see in 3D. To do this I created a “Test project” and went immediately to PcbNew (did not click on EESCHEMA).
I added one component, a Keystone test point. The wrl file is 358kB. It then takes 9 seconds to see 3D view. I added a second test point, it now takes 18 seconds. With a third one, it is around 27 seconds. Times were by looking at the clock on another PC, so not highly accurate.
Most of my wrl files are less than 1MB. I have one, for a RM12 pot core, that is 5.5MB. I use this component twice in my project.
So it is pretty clear that the issue is just the cumulative time to load all the parts. My project is large- more than 100 resistors, more than 60 capacitors, 20 SMT ICs etc. So even if each of these takes only 10-20 seconds to be added to the 3D view, I can see that the time will add up!
The processor is a Celeron CPU, J1900 @ 1.99GHz. 8GB of RAM installed. Windows 10 Pro, 64 bit. Updates are current. Computer is an Acer.
All of this was with the nightly build from March 24, 2018.
For the same test point, it takes also around 9-10 seconds to show the 3D view from the Footprint Editor.
I monitored the CPU usage and RAM in the performance monitor. CPU is around 7-18%, Memory around 3.9GB, so about 50%. This while the 3D view is being generated. Actually the amounts stay pretty much the same no matter what is going on.
Yes, I agree, the 3D view is an important tool, now that I have a taste of it on my faster machine, I really am addicted!