It shouldn't take that long. I would try to do a Save As and try again. Often times when you are just updating the same file it tends to get bloated. A Save As might clean up things a bit.
> It shouldn't take that long.
There are lot of things that ID does that should not take nearly as long as they do. Index generation is just a more extreme case.
> I would try to do a Save As and try again.
Save As which files? The index file itself? Or all of the chapters (there are 31)?
Using Save As is an old PageMaker trick that worked well for both size reduction and stability. I have not seen the same benefit with later versions of ID.
I haven't used the index recently. I did one a while ago (using CS6) with a book similar to yours but didn't see the delay issue. It might be worth it to Save As each chapter. Let's see if somebody else here has other suggestions to tackle the issue.