Using Shared Compendiums and deleting the now-exported actors should work in most cases. However, it’s possible that something else might be responsible for the size of the actors.db file 
I think the best way to figure out where the size is coming from, is to actually open the actors.db file on your PC after an export, and look inside of it using a text editor. The article here should be able to help you get to the bottom of it!