I am editing a book using track changes in MS Word 2013. The book has almost 5,000 edits and MS Word is running very slowly. Would it help to speed it up if I accept the changes? Any suggestions would be appreciated.

Yes, it would speed up scrolling through the document. You may want to save a copy (with all the changes still marked) first.

Using styles for all or at least most of your formatting will speed things up as well. Understanding Styles in Microsoft Word