I think you have a good chance of breaking the 20 mins barrier. But let's break it down on what you will need to do to achieve this goal. With 22:30 5k you are averaging about 7:15/mile, to run 19:59 you would have to average 6:27/mile. So, we are looking at you running about 48 seconds faster per mile.
I would suggest that you increase your mileage (run for at least one hr every day), and try doing some tempo or fartlek workouts, a good tempo for you would be doing 4-5 miles at around 8 minutes or faster if you can.
Fartlek workouts are great ways to simulate races, so I would also suggest that you should do some at fast paces to simulate races. Ex: 3 mins fast at 6:30/mile pace then jog for 3-5 minutes.
hope this helps!