He Should have spent 10 of the 15 hrs being sure to center the wings... Good News !!!! Cover up / add on to balance the wings will work . Just use another artist . Will be nice when done.
That tattoo couldn't have taken 15 hours. Unless a) Your artist takes constant smoke breaks. or b) Your artist has a handicap of some sort. Nice tattoo, but I highly doubt it took as long as 15 hours.