You can ask both KLM, Norwegian and Scandinavian who all have 18-25 minutes as turnaround time.
A full service turnaround of a 150-200 pax jet is not possible on continous scheduled basis in less than 20-25 minutes. I know it... (I fly those things
) The key here is that it must be able to be scheduled throughout the year. Sure, you can easily do it when you have no service and only a handful of pax, but it is a different story.
AWS turnaround is modelled to be always a full service turnaround with fuelling, cleaning, catering etc. There is thread in feature req forum about variable turnarounds where the time is dependant to the flight duration .. ie. a short domestic sector can turn faster since it does not need fuelling and so much cleaning etc.
Again, not a bug, the current system works just as intended.