FPS Movement Incredibly Laggy

Hey everyone, Very new to unity, was using blender for all the game engines but now only using it for modelling. Anyway I started by adding a smallish terrain (20x20) And added the FPS controller. Now, the camera movement works fine, but when I move with WASD it is horribly laggy, like 2 fps, and when I stop moving, the camera movement is un-laggy again. I even tried to Build and run it, but still not working too well. How can I fix this? thanks!