Has your toilet always been slow to refill? If so you have low water pressure and if you go to your local hardware/ plumbers merchant you can get a replacement plastic "nipple" (sorry can't recall the technical term!) suitable for low pressure which can be exchanged for the ex. one in the ball cock float valve. The low pressure "nipple" has a bigger hole to allow more water through- should speed up the refill rate. Check also that the float is not punctured (holding water) and is free to move up/ down inside the cistern.