You model is indeed getting on the large side at 143Mb for SU to handle easily.
How many faces, edges, groups and component instances have you (see Window/Model Info/Statistics)?
SU on a reasonably powerful machine can cope with files up to around 100Mb, and millions of edges and faces. Your file size is a bit bigger than that, and into the size where SU starts to struggle unless you are carfeul.
If you have downloaded many of the components from the 3D warehouse, it is very probable that they are seriously over-detailed, especially if they have merely been converted from manufacturer’s original CAD files meant to show how the product is manufactured. Many have internal parts shown in full detail, even if they will only be viewed from the outside, and even if drawn from scratch in SU, may have far too many segments in circles for the level of detail you need, or grossly over-large textures.
You can also check each component in the Component Browser - select one in the browser, then click on the Statistics tab. It may be slow to get the Component Browser open in a large model.
You can use Layers to make the model more manageable while you are working on it. Assign layers to components you don’t need to see while modelling, then turn them off
I’m working on a model of over 400Mb file size, with almost 75 million edges and over 30 million faces, a million component instances, and over 100,000 groups. With appropriate layers turned off, it is manageable, but only just, and my machine struggles a little even to orbit and zoom. The developer whose model it is has a more powerful iMac than I do, and finds it more easily workable, but ONLY with careful choice of layers to make visible while modelling.
I had to simplify for him many items he’d downloaded direct from the 3D warehouse, to prevent more serious overload - see for example this thread:
Good practice is to download each component into a new SU model, and inspect it before inserting into your main model. Simplify if needed (in my experience, it usually is!).