I have worked on big projects were there were 15,000 parts in CAD, but most of them were not structural. If you suppress all the nuts, bolts, washers, and screws, all the electrical wires, all the labels, etc. How many actual structural parts are there?
The reason I say suppress all the nuts, bolts, washers and screws is because, though they are required to hold the structural parts together, they can be removed from the export of geometry into Mechanical for a simplified model of the product. Connect the holes on each side of a nut and bolt connection with a Fixed Joint for example. There are ways to automatically generate hundreds of Fixed Joints using the Object Generator.
Most big projects are built from subassemblies. A simplified version of each subassembly can be built for the entire product simulation. Global loads are applied to the entire product. A detailed model can be built of each subassembly. The displacements in the entire product model at each subsystem interface are used as input loads to each subassembly. Ansys has a nice capability to automate this. In that way, a reasonable number of nodes are used for the simplified version of the entire product, and then a similar number of nodes can be used to make each detailed subassembly. If all the detailed subassemblies were put into one gigantic model, it would be too big to solve. But each subassembly is solved one-at-a-time so you can work your way through the entire product at a detailed level after you have built the simplified version of the entire product.
If you have composites, maybe the structural parts are held together with adhesively bonded clips. In a simplified entire product model, all the clips are left out and shell elements simply share nodes at the intersection of one panel to the next where the clips used to be. In a detailed model of a local area, the full detail of the panels, clips and adhesive bonds can be represented.