Infinity Irs Betas vs Legacy Focus Se

Which would you choose and why. The listening room is 15 by 18 . Thanks for any input.
Can't speak to the Legacys, but there is no way I would put IRS Betas in a room that small.  They need a LOT of room to reach their full potential. The other thing to keep in mind about the Betas is that you may have trouble getting replacement drivers if needed. 
Unless, of course, you meant 15 by 18 meters!
My room is only 12X20 and I would like to hear from others about small rooms and biggest practical speakers.
Magico S3 used would be better.

rcprince, that's one of my and I guess many others' "American Dream" to default to meters and grams someday and get "Back To The Future". Can American Dream come true?
I have a pair of epsilons in a 15 x 19 room and I feel it’s way too small for the speakers, the problem with big speakers is that in a small room you can’t place them far enough apart making the listening position so close to the speakers that you start to hear individual drivers instead of the whole speaker, If you have your speakers 7 feet apart then the listening position should be about that same distance away from those monsters, In my opinion... way to close, they need a much bigger room to sound their best.

Cz, I think we as a nation are too stubborn for that, as I believe there has been a movement afoot for years to do just what you're talking about and it still hasn't happened.  I would probably have some problems, since I play a LOT of golf (about 270 rounds a year) and would have to get used to thinking in terms of meters rather than yards for my approach shots!

I'd go with the Legacy Focus' speakers. Very efficient, loves tube amps. Very musical and relaxed presentation. I've heard the Focus' a few times at three different friends homes ... sounds great in all three places. I use a pair of Legacy Signature III's and love them. If I were to upgrade, It would be to a pair of Focus 20/20's   not the newer ones ... the older ones. 
For now I will use my Irs Gammas as they seem to be a better fit for the room size. I don't know if the Legacys would better the Gammas or if it would be a sideways move.

those Infinity speakers require a very large space to open up and sound their best.  Keep me posted & Happy Listening!
The Infinity IRS Betas will overwhelm that room...physically and sonically.
I own a set of the Betas.
Still haven't heard from OP about meters tho.
I own a pair of Legacy Focus 20/20's, and my room is 16x18 feet. (5.3 X 6 meters) ;) Placement can be an issue, getting them to triangulate with the listening position, but, I think I've got the sound stage starting to come together. And while they may claim efficiency, they can consume much power! I like all manner of music, from Spanish guitar to Tchaikovsky, but mostly rock. And it will do it all! But! If you want them to rock, you need some power! I've got a Forte' Model 3, 200 wpc @8ohm. And it was running out of steam trying to get rock and classical up to (near) realistic volumes. I've added a Crown 450 watt PA amp I borrowed from the band to power the bottom half, and it helped considerably! But, it's just temporary until I can get a real amp behind it. I had my mind set on an older Krell 300 watt, or something similar in an A or A/B amp. Now I'm thinking perhaps a 1000 watt class D amp? Or the D-Sonic 1500 watt monoblocks? Believe me, neither one will be overkill.  (Anyone out there with experience with such a pairing I'd be interested to hear?)

I love the speakers! They are so smooth in the upper registers, and are truly full range. Orchestral crescendo's do not sound lacking on either end, and bass slam is not muddy on rock music. I've heard better soundstaging and 3D imaging, say, in a set of electrostatics, but the Focus's carry the weight of large scale music, and being a bass player, it reproduces bass more clearly and plainly than any speaker I've owned.  I've never had a set of speakers that allowed me to hear what the bass is doing so well, I can hear the bass player's fingers on the strings! And instruments that low in frequency are just as clear and out front as vocals and guitar and piano in the midrange. I'm not saying they are bass heavy, on the contrary they are very balanced top to bottom. Cymbal crashes sound like brass, not breaking glass, with excellent decay and shimmer. 

I've heard the Infinity's, but many years ago, so I can't claim a side by side comparison. The Legacy's are easy to love, and you see very few of them on the used market compared to many other large speakers of their kind, so they seem to be making a lot of people happy.  Your listening habits can influence your decision, but even though the Focus's are large, they also sound great at low volumes, they don't get louder, they get bigger. Or is that a function of the amp? But I do not feel they are too large for this room, maybe they would sound better in a larger room? But they sound pretty great as they are..