* "Billy Macgregor" is played by Andrew Strong. He was a real-life singer who was discovered for the role.
* "Joey" is played by Bronagh Gallagher. She was also a relative newcomer to acting at the time.
While "The Commitments" isn't specifically about a movie called "Joey", it's a very popular film and those characters are quite memorable. It's possible there's a bit of confusion about the film's title or a similar movie with a similar character name.
If you can remember any more details, I might be able to give you a more accurate answer!