I am in IT and we learned that a large majority of our users have duplicate photo libraries. This is the result of Photos App converting the iPhoto library but not removing the old library. So any on with a large library, will have twice the space taken up.
Make sure you check your Pictures folder for an older iPhoto library and delete it if you have converted. If you already knew about this, excellent!
Make sure you check your Pictures folder for an older iPhoto library and delete it if you have converted. If you already knew about this, excellent!