Les, here is what I do to avoid this problem. First, when I designated my root music folder as the default, I did not check the box for "Subdirectories". Second, I use the root folder only to store incoming files (i.e., those unprocessed or in process). That means that the root folder rarely holds more than a hundred files and so loads very quickly. In effect, I use the root folder as my "new additions" folder. After editing, I move those files to an appropriate sub folder. This system has worked well for me for many years.
Of course, and from time to time I do this. For me that means simply checking the box for "Subdirectories" temporarily. However, whenever possible I use queries from Windows Explorer to save loading time, as I discussed in this post: