Try to simulate a specific portion from your geometry. Most of the time in structural mechanics there are some parts of the geometry which are of most interest. That’s why, mostly simulations are done on simple parts of an assembly. Your model will be hard to setup and will take lot of time to simulate.
Once you have selected an interesting part to simulate, try to simplify it as soon as possible by removing unnecessary details and merging the solids which will have either same material or no physical contact involved. You can have a look at [this] (Merging solids in Onshape and meshing) forum post for more info.
In order to simulate this case, you can have a look at [this] (https://www.simscale.com/projects/stadlerj/suspension-structural-analysis/) project.
Hope this helps. If you have any question/s, feel free to ask.