Turning an object into a block is fast. Then placing it several times in the correct location and orientation will take time.
Generally, yes. But you’ll want to make sure that you join the correct surfaces with each other. I haven’t looked closely at those surfaces but I imagine there might be cases where simply selecting everything and running Join on that will create objects that are not what the intended outcome would be.
So, yes, it will take time to clean this up. If putting things on a different layers and just turning those off when you need to work with a limited number of objects, that might be a faster way to deal with this. But it all depends on what you need to do with this file.
-wim
Hello- you have a very large number of quite complicated objects in this file - 60,000+ surfaces etc etc. This appears to be almost all furniture and details, not the underlying model. What I would do as a ‘cheap’ way out is to make lightweight mesh versions of say the chairs and tables and then Join all of the similar objects into one mesh. Join all the mesh plants into one mesh etc. But really, the way to deal with this is to open the objects that you have inserted multiple times as individual files, optimize (say by meshing, joining whathave you) then inserting these as blocks. Some of the objects, like the toilet - are vastly more complex then you need and for that matter poorly made so much more memory hungry at the geometry level than they need to be.