Depends on what you want this movement to look like.
If you just need constant speed, you can do this without any behaviors:
On every tick
Character X<15 : Character move N*dt pixels
You can use lerp (very fast start, slows down as it gets closer to position):
Character set X to lerp(self.x, 15, dt)
Or try the new Tween behavior in C3 runtime, with it you can make different cool effects - acceleration, deceleration, bounce, etc.