You may never be able to break 2:30. Your ceiling might not be that high. 22:00 6k after minimal training is very impressive, but there are plenty of high school guys that do the equivalent of that in their first year or two of running.
As someone previously stated, 6k is worlds apart from the marathon. What's the longest run you've ever been on? I know you said you wanted to do some 120-150 minute runs in training, which would be about spot on for marathon training, but if you've never run that far, it's going to take A LOT of base mileage to get used to running that far, let alone racing that far.
On top of what I've said above, you have to stay healthy. I don't think you've run enough to just increase the mileage to the level you need to run 2:30. Train for a few years and start with 10ks and half marathons, then ask us again if you can run 2:30.