I do not know whether it is traditional or composed, but it seems quite likely to be traditional. I believe that some Irish musicians playing this tune
This carol was written for Christmas of 1829 by Jose Pacheco, master of music at the Mondoñedo’s cathedral. It uses the same key signature and tempo of a traditional "muiñeira" - mill dance. Thanks for sharing it. It needs a few changes, though. Carlos Núñez does a perfect interpretation of this tune.
Re: Galician Carol
Not sure, but I think the high b in last part - third measure should be flat…