Hi Tim,
Wow! It's really amazing how many flowers your yucca filamentosa x rostrata (Benny's hybrid) has, really beautiful! 15 feet tall? your yucca elata is quite the beast you say it is, maybe with a good ladder it may be possible to pollinate it, good luck if you decide to do it
This year I have 3 stalks ready to bloom from my filamentosa, I will try to self pollinate it so I can learn and be ready when my other yuccas will flower (4-5 years!)