There are many factors that can affect the performance of your connection.
You may check out this article: Slow speed issue
Furthermore, you are currently subscribe to the NBN12 plan which is ideal for 1-2 users. This plan is used for basic internet activities such as email and browsing.
If you are using a WiFi connection, signal interference can play a part. We've created some articles that will help you improve your home network.
Should the issue persists, let us know of your most convenient time to receive a call so we can organise a call back to be made from our Technical Team for assistance.