Welcome to the community!
ADSL2+ connection speed is based on the copper line distance going to the exchange and your location is 1332m away from the exchange ( This can be seen by visiting this link http://tpg.com.au/maps/ ). The fastest speed you can get in your location is in between 15-13MBPS.
The speed test result you're getting in your location is passing. Let me know should you require further assistance.