Curious to see how the different the picture is when dealing with non-renderworks viewports.   Open the attached file (sorry, it's quite large); it should already be looking at the sheet layer as per screenshot below; select all three viewports and press the "update" button to update them all.   On my M1 Mac Mini 16GB it took 2 mins 48 seconds.   1049605006_vportrendertime.vwx