brep bodies that are converted from mesh bodies are huge. and you have a ton of them. not generally recommended to work with fusion in this way (b/c fusion doesn't handel it well). plus most of those imported items have a lot more detail than would be necessary.
breaking the links will help performance. as will deleting the mesh bodies and converting the solids to DM features. right now you have them scaled 3 times, which also adds to the size.
even better would be to create simple models of each thing in fusion . then use joints to arrange in your model.
FYI-it's not necessary to add a new scale command when you want to change the size, just edit the existing one.