Your asking him to go faster than his (probable) 5K PR 3x a week. You have no idea what you are suggesting.
When I started running (1985), I dragged ass probably as slow as David most of the time. I was jogging/slogging/flogging myself through 9 miles a day as a complete beginner over the summer. Despite the sloth, nothing faster, I got to about 17-flat 5K fitness by my first cross country race. A few months earlier, I had only been able to race 10K untrained in 54 min.
Unlike David, I had fitness from a lot of cycling (10 hrs a week maybe); did close to 6:00 in P.E. for the Presidential Fitness Test untrained, so had some talent; and did 4x his mileage. But still shows you can improve a lot doing slower than 10 min pace as a beginner.