Well, the W18's in the HT2-TL compliment the RAAL tweeter extremely well, and since the W15 is just the little brother I'd imagine it will sound very similar, if not the exact same without the added bass extension. If I had upgrade right now and couldn't afford something from the SoundScape line, the Super-Charged SongTower's would be my choice.
Unless something has changed each speaker comes with a birth certificate but not an individual FR plot. If you asked for one, though, I'd bet Jim would happily accommodate.