Thiel Owners

The one series is made for small spaces, moving a fraction of the air.
Woofer areas are approximately 1: 10", 2: 50", 3: 75".

With a  room that size, the 1.5's will be too small. You're not going to fill the room sufficiently. The 3.5's requires an amp with LOTS of current and the ability to drive a 4 ohm load with ease. As long as you have that, it'll be very rewarding. And of course make sure you get the bass equalizer, an absolute necessity with the 3.5's

I used a Bryston 4B with mine. No distortion at louder levels.

The 3.5 is a remarkably good speaker. I’ve had 3 pairs paired to amps that were capable of 300 watts into a 4,ohm load.  I never came remotely close to that.  

The bas eq is indeed a must for making them sound as Thiel intended.  Though I’ve never blown a speaker in my life the 3.5 mids do not suffer abuse well. If you can make sure they’re working prior to purchase - the repair/investment is about $300 apiece if they aren’t. 

And worth every penny.  I had a pair repaired by Rob a few years ago. 

oblgny
You are the 3.5 resident expert. Thank You for chiming in my Brother.Not only did you own the (3) pairs, you had a plethora of gear constructed for each pair that offered a unique aural experience.  I can hardly await to read about your next Thiel loudspeaker acquisition.

Happy Listening!