A rough guide is shown here. That is on a perfect line in perfect conditions so I would expect you may get less than what is shown. The only way to tell is to run an estimate check https://www.dslchecker.bt.com/ using your phone number even then it my be slightly off.
EDIT: Just noticed that you have already been given this information in this thread that you started.
if you currently get 14/15mb then that is about 2/2.3km from the exchnage and if you are on EO line then that will be the distance from the street cabinet. using the chart posted by gg30340 shows a speed of <20mb on fibre