I think you'll find that new data gets written to the sd card, but that the old stuff stays where it was. File managers can access the Android folder, so check what's there - the dates in particular, both on internal and external storage. If the same files are in both places, it should be safe to delete the older one, but you could try renaming first - just rename back if the app stops working. Afaik, the Samsung file manager is a system app, so will be able to write to the sd card if you need it to.
If you're filling 16gb (or the available space) with apps, you've got one heck of a lot. Are you really using them all?
There are settings for the default storage locations, usually in Settings under Storage, but they may be a sub-menu. Exactly where seems to depend on the manufacturer.
