Fred,
Can you share your design with us?
The 3D images you shared aren't very helpful in seeing what's going wrong.
1 - Using the plug-in CopyAsNewFurniture allows you to copy (part of) your design and paste it in another instance of the program that is open at the same time. I do it every day: if it works on my computer, it should work on yours. Read the manual to see how to install it. The plug-in adds the function Tools --> Copy as new furniture to the menu, as I wrote before.
2 - The way you describe to copy (part of) your design (select all --> group --> copy as furniture ) does NOT describe an actual way of working in SH3D, so it is impossible to say if you do it correctly or not.
3 - If you suspect that your computer isn't powerful enough, you can temporarily make all tables and chairs invisible. This will reduce the workload for your computer considerably, and the program will react much faster.
EDIT
Below is a picture of a fast sketch design I made: a restaurant with a gallery. Just to show you that it is possible to do this with SH3D.
Hans
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Hans
new website - under constuction
hansdirkse.info
