A shared folder is using all of my Dropbox space.

Thanks for posting on the forum, FuriousPCDesigns. 

Keep in mind that, when joining a shared folder, you basically add it to your Dropbox account, which is why it takes up space from it like any other personal file would. You can read more about this in this Help Center article. 

Now, if you mostly need view-only access to the folder in question, its owner can send you a shared link instead, so that you don’t have to add it to your Dropbox account at all. 

Hope this clarifies things a bit.