One more thing - some external editors can increase the size of the edited versions considerably.
When I edit a photo with Luminar, for example, the saved JPEGs are huge.
Here is an example of sorting the jpegs in the resources folder by size:

The largest files have all been edited in external editors. The "render" file on top has a whopping size of 75.5 MB, but the original in Photos is shown as a JPEG of just 2.2 MB.

If you are using external editors or photo editing extensions, they might increase the size of the library considerably.