The Fifteenth Brigade included the English, Washington and Lincoln, and McKenzie-Papineau Battalions. So the "Hurrah for the Fifteenth Brigade" version is what Anglo-Saxons in the International Column (Communist) sang. The more pompous one sounds like an official version.

Most of those songs had multiple versions. An anarchist, who unfortunately could not carry a tune, once sang me a version of Si mi queires that began:

"When the haliputa Franco dies, and you pass his tomb, always remember to spit!" and goes on:

When you go to Barcelona
The first thing you see
Is the Communist heirarchy sitting down in a cafe.
They have blankets, and nice, warm coats,
But here at the front you can see our ass!