Hi @cylinyu1 ,
TPG NBN plans are available with download speeds of up to 88.1MBPS (Typical Evening Speed of TPG NBN100, while ADSL2+ Connection speed is based on the copper line distance going to the exchange has a maximum potential download speed of 24Mbps.
Once an address has been declared as NBN-ready, we can only provide NBN service for new sign ups. Customers who are currently on ADSL gets to keep their ADSL connection until such time that the line gets decommissioned or they decide to upgrade to NBN. However, once they've upgraded to NBN, they can no longer go back to ADSL.
What speed you're getting with your current NBN? Feel free to post the screen shot of the speed test result on this thread for reference.
In case you experience speed issue on device(s) connected via Wi-Fi. You may find these article helpful.