They do not have them hooked up at Best Buy so I cant listen.
thats the only difference I could find, and the T15s will fit my speaker stands better.
I have no idea how the Tsi's sound but the T-15 are cable as rears. I initially used them as fronts until I upgraded. Don't expect any bass and I had them crossed over at 100hz. If you want more information on them search for info on the Polk R15. Identical driver and tweeter. The only difference is the color. The match well with my Monitor 50 and CS1 if thats saying anything.
I actually just installed the T15s I picked up on Black Friday as rears today. I ran into the same problem you did, so I secured them to the stands with a couple small wood screws. Yes, it left two small holes in the bottom of each speaker, but it was cheaper than buying new stands and much cheaper than buying a new set if they were to topple off the stands.