Sure it is possible. If you aren't trying to be at 2:22 this year, then move up to 75-85 miles per week and hold that for a few months. Include a balance of long intervals, long fartleks, hills, fast distance runs, and races. Once you can handle that, you can make a determination about what is possible. You current training of just 55-60 miles per week limits your perception. If you think you can do it, then become a marathoner and do marathon workouts in cycles of 3-4 months, alternating with 10km training in equal cycles.
Lack of speed over short distances doesn't limit you from doing well over long distances as many would have you believe. I figure the minimum speed you need to run a 2:22 marathon is 30:45 for 10km or 14:47 for 5km; if you have natural endurance ability and go run long distances without a problem.
My opinion: Regrets eat you up. Go for it. Tinman