I just purchased the 15t for my MTB...
These are great cogs, well made, fit perfect, bolts included, and no lock ring The 15t does have a wee bit of chain interference on occasion, but very very minimal.
For anyone with a disc hub that may want to try MTB fixed without building a wheel, be sure to consider one of these.
I run 32x18 free on the trail, but have found without owning a car this year, getting to the trails has been an issue, 32x18 spins you all the way there. So I bought the 15t so I could ride fixed to the trail and flip it over or punish myself once there.
32x15 on a 29er comes out to about 62gi, so not the fastest, but a hell of a lot better than 32x18, and running fixed makes it that much better.
Cannondale has a 4 bolt rotor design? And I'm sure lots of companies are making those 4 bolt rotors...
I hate when companies pull crap as such, why can't we find one or two standards and stick with them
As far as the 32x15, commuted to work on the 9er, not too bad. Not ideal, but I didn't feel like I was spinning a hundred miles an hour and I kept my speed up enough that I got to work in about the same time as usual.