Right. It's typically only used for hunting and cavalry. Even most lighter types used a belt-hook.
15 shots a minute for a longbow, however, means 15 bad shots, a tired archer, and running out of arrows. I doubt people really did it often.
The video guy is doing twelve shots a minute, so I'm not sure it would be that bad.
But it would be something you'd only do if you were firing as fast as you could pull ( with the result looking like this http://www.youtube.com/watch?v=vAUp1ripJLE ), rather than for well aimed shots at individuals/targets.
Still, in the right circumstances, the crossbow rocks - I hate to say this as a longbow fan, but it really is a solid weapon. Add a pavise for defense and its not even that bad vs. the longbow (the reason we see crossbowmen mowed down in the HYW by longbowmen is those being absent - along with incredibly inept use of the Genoese crossbowmen by their commanders).