. I'm not using just Photos. I am again running out of disc space.
Sorry, I don't understand. What are you using right now?
Have you migrated your Aperture library to Photos? Are you still using Aperture? What happened to your referenced image files in Aperture?
If you migrated a referenced library to Photos, it would have kept your referenced originals as referenced, unless the external drive with your referenced files is not formatted MacOS Extended (Journaled).