As soon as two items overlap the software tries to determine if one encloses the other, and with the complexity of these, that’s not simple. When you have 20 items that are all very complex, it needs to check every one against the other 19, and with thousands of points each, it takes some time.
Having said that, I can probably remove this computation for the shapes in question, because they’re all fills, so it doesn’t matter if one encloses the other. I’ll look to see I can do this safely. If they were lines, then the “Cut Inner Shapes First” restriction means that check needs to run.