Hi,
Thought I'd pass this on.
I created my first, multiple gallery with 5 galleries. It took so long to generate because there were over 100 images. So I tried something else. I started over and created the main gallery as I wanted it and then added 4 dummies. For each dummy gallery, I added just one image, and proceeded as usual with all other steps. When I generated the gallery, it took no time whatsoever.
I then went to the first that I created that had over 150 images, opened the folder and copied folders 1, 2, 3, 4 (the program numbers from bottom to top) and replaced same folders in the trial. It worked perfectly!
So, you can create each gallery separately and them add them to the gallery with the dummies without the long processing time and chance of your system freezing up. There is another thing that would need to be done. When you create only one gallery, the folder that needs to be copied will always be named - 1. So you would have to renumber it to match the correct position in your multi-gallery.
This also helps me to be able to add a gallery that has already been created, so it doesn't have to be done all over again.