I installed Catalina 10.15.2, and I have two accounts both over 60GB of music. For one I set the preference to Copy files to media when adding (image), which gave me the “Import” option (image). Here, I had a memory issue when adding 10 albums the data was copied and songs appeared in the browser, but then Music used up all the memory doing something else and importing took a lot of time since I had to use small batches. For the second account, I copied the music manually instead, which gave me the “Add to Library” option, which was faster and more efficient. What is the issue with the “Import” option?
Check the information in this link
Hope it helps to understand what is going on