The T15 is a nice engine.
I race on a short technical track and the T15 was nice on that track.
The 18 CV-R is more powerfull....more then needed on that track.
When you race on a track then the OS TZ's are overkill...maybe nice for parking lot bashing.
The CV-R is an easy drop-in, but the TZ's need some modifications.
I only purchased some Wolfpack Radicals adjustable engine mounts (great mounts!) and popped the CV-R in.
Actually...mine is a CV-RX and I can still use the rotostart.