I am an NBN customer and I called Optus to enquire about increasing our speed. I was told that we were able to increase the speed for no extra cost and it would take 24hrs. I am still on the same speed 4 days later. Currently running 28mps according to my DSL router, 15.09Mbps according to Speedofme, 20.74 according to SpeedTest and 10.64 Mbps according to OzSpeed Test. All different speeds all in a matter of 30secs to 1 min of each other.
Could this be due to having an older home and the NBN running through the old phone line? Or is there issues with the speed?
I am trying to stream my uni lectures and I keep buffering.
Those speeds are adequate to stream most things, so something else is wrong. You must be getting periodic dropouts and packet loss.
Speedtest is probably showing the upper limit properly, so keep hammering that. The others are probably congested. If you are using a PC, install something like Networx and download something large (Win7 SP1), and look at the data. See if it stops.
Figuring out why NBN could be wrong is difficult, esp. with Optus since they don't call back.
What speed were you on? 25mbps?
Old phone line? Are you on FTTN?
Its possible your line can't go any faster than around 25Mbps. Optus should be able to test the line for max speed (if FTTN).
Its also very possible Optus just haven't upped your speed yet. Sometime it can take a few goes back to get it to stick.
The streaming issues might be because of something on the Uni end. As @10000000000GB says your reported speeds should be enough though. Try streaming some HD youtube videos and see if you get buffering. Also try doing repeated speed tests with one tester for a little while (every minute) to see if you get much variation. Finally congestion in peak hour may cause issues, try speed test in off peak to see how stable the line is.