If your Viewport in Thea Render Studio is sluggish for large scale model with heavy geometry you can opt to enable option “Use Level of Detail” and “Limit max drawn triangles (per model).

These two options will decrease the workload on your GPU at the cost of lower detail for the models being drawn in your viewport.

To enable these options you need to select from main menu toolbar, Customize > Preferences and then enable these options in Viewport panel.

Please note that “Max Drawn Triangles per model” specifies the number of faces being drawn by the real-time engine and you can manipulate the triangle count according to the level of geometry resolution you desire.