Model conversion from one format to another (especially CAD or engineering content) can take a long time depending on how much data that it has in it. This is primarily due to the fact that data conversion has to take place to convert the information from one format to another and then build the proper unlying 3D geometry.
Unfortunately the only way to really make the import process go faster that I have found is to have your data broken up into more files (such as by layers, instead of one larger file).
In 3DS Max 2019 a new Importer was released for importing CAD/engineering data. With this importer the quality slider plays more importance to the resolution output of the data that is being imported. This can affect your import time at the cost of more mesh resolution. Hence another good reason why you should have your data broken up if you can do so, because it will enable you to have the data resolution where you need it.
In regards to your question about "speed" after it has been imported there are a few reasons for this and some general suggestions...
1. CAD data is usually messy, with every bolt, rivet, washer, spacer, etc. included. While all of this looks great, each object in your scene causes more for the software to deal with and calculate. What I do (and this isn't a guaranteed trick for everyone, just something that works well in my work style) is try to consolidate this data by removing what isn't needed and merging/attaching similar data into a single node.
2. CAD data will often come in unoptimized. Often requiring a vertex weld, or even rebuilding mesh data for it to be more optimal. Just be careful about your normals being changed.
3. 80 million polys will cause 3DS Max to work pretty hard to think about how to display it (this is a given, its a lot of polygons spread along a lot of objects) but it can do it with a workable framerate. Max versions from 2017 onward have gotten better and better at how they handle this data for performance. But to help improve your performance with this it really IMO comes down to is using layers to hide or freeze content that you do not need to interact with at this time. You could also maybe try Xrefs but that is up to you.
4. This all requires significant time on your part to put into the file, but it can be well worth it in the end.
