You have a total of about 21000 (logically visible) nodes in your scene which is not the lowest valie ever but still fairly medium. If I estimate well enough, I would guess the number of objects in the scene to be around 100. That brings us to about 200 nodes per object. With the objects you already looked at in more detail with 10 or respectively 24 nodes, the node count must come from somewhere else. There are two or three objects with standard graphics (assembly or dismantle) for which I know the typical number of nodes well enough so that we can rule them out, too. I think it might be worth a second or third look for objects with complex graphics. Another thing that points in this direction is that you model size is really large (240MB it was, right?) for a model with so little vislble graphical content.
Now let us look at your graphic adapter. The adapter (and the driver) certainly actually is rather old. One hint you can use is the text in the right part of the frame rate line. Your adapter/driver combination supports OpenGL versions up to version 4.2 (that is the first part of the text) and is described as "Compatibility Profile Context" which (according to my own search - I had not read this before) just means that is also supports older OpenGL versions aside the new ones. (I would have expected this to be always the case so I was a bit surprised that it even happens in another fashion). In general, for years, many considered ATI (or now AMD) adapters to be much more error-prone than NVIDIA adapters when you have some sort of CAD or similar application (also including performance issues). I had my share of problems myself almost a decade ago. In recent years, I came to the impression that both manufacturers converged regarding that matter. Graphic adapter issues seemed to become less and less an issue. This however does not mean that it certainly is not the case in your case. A good thing to do would be to run your model on another machine if that is feasible.
A final word about graphic adapters, OpenGL and the OpenGL level: If possible (and from a look at the screenshot, it seems that it is possible), use at least 3.1! Especially 3.0 (for some unknown reason) is known to be a really really slow OpenGL level. You can change this in the preference dialog on the 3D tab. While you're at it, have a look at the screen coverage threshold. Increasing that value can improve your render performance, too. The value basically specifies how (visually) small a single graphic node may be to be not rendered at all.
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