(Since Taña has indicated that she doesn't intend to post an answer, I'll do so. The translation suggested in her reference is correct.)

"Registro" is "stop" in English. It's in many dictionaries, and I provide some references in this previous question (the other way round):
https://www.proz.com/kudoz/english_to_spanish/music/6195925-...

The 2' (2-foot) part means that this is a stop in which the note that sounds is 2 octaves above the note played. I'll repeat what I've said on this on the other question, on the 8' Regal stop. An 8' (8-foot) stop is one that sounds at "unison" pitch: the note you play is the note you get. The name refers to the approximate length of the pipe(s) for the lowest note. The shorter the pipe (and therefore the vibrating air column when it's played), the higher the note. As with a string, half the length means an octave higher. So a 4' (4-foot) stop is one that sounds an octave higher than the note played, a 2' (2-foot) stop sounds two octaves higher, and a 16' stop sounds an octave lower.
https://en.wikipedia.org/wiki/Organ_stop#Pitch_and_length

So with a two-foot stop the note sounds two octaves above, and an interval of two octaves is called a fifteenth in musical language, just as an octave is called an eighth. If you start, say, at C and play all the white notes going upwards, from C to C (both inclusive) is eight notes, and fifteen if you go two octaves.

So a quincena, which is an old-fashioned way of saying fifteenth, is by definition a 2-foot stop. In this sense, 2' is redundant, though I wouldn't leave it out.

A stop called Quincena is called Fifteenth in English, or sometimes Super Octave (or Superoctave). You could leave the name in Spanish, but I think I would translate it; it's a generic name.

http://www.organstops.org/f/Fifteenth.html

And see Taña's reference for confirmation.