Well, all the rotate behavior does is the same as a event like this:
Every tick: sprite: rotate clockwise speed*dt
With just one object, there isn't much you can do to make it faster.
How is the performance bad?
If you're getting a low framerate then you might have a blacklisted graphics card. If you can update your driver it may help.
If instead you're getting a rotation that's not buttery smooth, then it's a current browser issue. You can have lots of sprites/events/behaviors or very few and it doesn't affect that. Chrome supposedly has a fix coming in a newer version, but other than that other browsers have varying degrees of stutter. Once one solves it well I'm sure the others will follow suit.