My instructor has quite an easy way of completing the left reverse turn. As soon as you start moving (with the clutch held down low) keep an eye out in the back corner window. When the kerb is about 4 inches in, turn the wheel three quarters to the left and then as the middle of the rear window hits the kerb, straighten the wheel up. The philosophy that my instructor uses is:
Keep the clutch low, the car goes slow
Raise the clutch high, see the car fly.
Even by reducing pressure on the clutch by a fraction, it can greatly reduce the cars speed. The examiner isn't looking for you to complete it as quick as you can. They are looking for you to do it safely and effectively. If that means going really slow, then so be it.
Remember, clutch low. If you feel the car starting to go fast, press the clutch down by a fraction of a fingernail