They can get very heavy if it lives long enough, thousands of pounds. If it lives long enough it will reach 15 ft probably in 5 years or so depending on how happy it is.

May i suggest a palm for you? since you seem to like pinnate "feather palms" and are limited to space why not try a Chamaedorea radicalis "tree form"? its a very hardy small feather palm that can survive temps just below 20f. It likes part shade so being indoors for the winter wouldn't faze it as much as a queen.
Look them up. they are beautiful palms and hardy :D

goodluck
eric

I like them, but where can I buy them? I would need a larger one because they are probably slow growing. Someone mentioned that queens are really light, (i posted this just to confirm) so would they really weigh a lot when they're 15 feet?

hope this helps
http://www.junglemusic.net/careandcommon.asp?species=Chamaedorea%20radicalis

Queens are light at a young age, all plants are. But queens arent good for being potted long term. im guessing a healthy 15 ft tall queen would weigh around 200+ pounds.

I like the radicalis, but I can't find a way to order it. How easy is it to protect it outside or in other words what would i have to do?

If you can find one i would suggest you bring it inside whenever temps go below 23f. if you wanted to protect it outside you could but bringing it indoors would be so much easier. Thus the reason i suggested such a compact palm in the first place.