Where are you seeing this? " ... the Photos app is holding my 45GB of data"
Are you still seeing photos in "All Photos" or "Recents"? Then you may just have removed the photos from your albums, but not deleted them from the Library. Try to delete your photo while viewing a Library album, like "All Photos" or "Recents", and nor while viewing one of your own albums.
If you have items in Photos that have been synced from a computer with iTunes or the Finder, you cannot delete them directly on iPhone or iPad. You have to delete them by syncing again.
Also, if you are using a shared iCloud Photos Library, you can only delete the photos shared by you, not the photos shared by others.