There isn't going to be something "faster" than Update(reference), that runs once per frame:
Update is called every frame, if the MonoBehaviour is enabled.
If your frame rate is half a second per frame, then you'll get a half second delay. You'll need to perform some optimizations if you want faster response. Make sure you're MonoBehaviour is enabled, and you're not running Update as part of a Coroutine. You can try creating a new project, and just putting your code into a new script on an otherwise empty object.