It seems odd that if he were building a home theater that he would have a screen with 10' by 15' dimensions. For a widescreen he would make the screen 15' by 8.42'. That leaves over 1.5' of wasted space. But there are plenty of light cannons out there that would light up that size screen. The BenQ SP890 is what immediately came to mind. You would need a throw distance of just over 24' to do it with that PJ. You can go to Projector Central and search by feature to get a list of PJs that will work with his screen size and throw distance.
A 15 foot wide screen doesn't need a light cannon if the fabric is right.
I'm lighting a 13 foot wide screen on low lamp with brightness to spare (95ES), due to a high gain screen. My projo on high lamp (which is fairly average lumens) would light a 15 foot screen if it were HP or similar material.
So maybe if you got two projectors and dual-output,... assuming they were lined up right, it could give you enough light...Anyone know if this would work?
If this would work, you'd probable want to go single chip DLP or else you'd have to deal with panel alignment across two projectors... I'm sure at this size, screen door effect could be a factor if you're too close to the screen (unless you get 2 of the sony 4k projectors!!)