Not from your phone, no.
If they've synced back to Google, head here:
https://www.google.com/contacts/u/0/
On the left hand side of the page, there's an option to Find Duplicates. You can merge/delete from there. After a couple of minutes (or a manual sync, they should tidy themselves up on the phone).
I'll move this to the S6 Edge section, just in case the guys there know of a way to do it on the phone.