Where do you get 15 flat 5k speed from a 12 flat two mile? I dream of breaking 15 flat someday but I was able to gut my way through a 12 flat two mile off of zero specific training during high school. I had just been playing soccer with my team all summer. On the first day of high school preseason camp we did the Cooper. 1/3 of us managed two miles. By the end of the season only the keepers couldn't do it.
When I was playing soccer I ran 11.8 FAT. At better tournaments, while I was playing either on the wing or up top, there were always defenders who could match me step for step. DEFENDERS, not strikers. Everyone on my team raced against each other in sprints once per week and I was about the fifth fastest. We weren't timed, but low 11s seems plausible. These were 16 year olds.
As far as the "only 7 miles in 90 minutes" argument goes, I suggest you try playing soccer. It's basically a 90 minute sprint workout with jogging recoveries. Actually, it's harder than that because you're not sprinting in straight lines. Also, if you've never been a sprinter you might not realize this, but running at 100% is so much harder than running at 95%. Soccer players cover a lot of distance at 100% and that can trash you. Also, you're changing directions constantly, you're crouching low on defense. It's utterly exhausting. After taking a few years off from soccer and developing into something of a distance runner (2:58 26.2) I joined an amateur team last year. I thought that all of the running I'd done would make me so fit for soccer. Actually, I was sucking wind the entire time and I couldn't walk up or down stairs normally for a week.
I should also mention that although running a fast 5k is not what soccer fitness is about, I've seen plenty of respectable distance efforts from soccer players. My brother was a 4 year starter in college but his speed and endurance were considered his achilles heel. His body fat (tested in a tank at a lab) was 4% and he ran the mile a year earlier in 4:50. I also know of an oft injured, 35 year old minor league pro who broke 3 hours in the marathon. A kid that I played amateur ball with ran 48-49 in the 400 (probably the best distance for soccer players). Another teamate of mine debuted in the 800 at 2:02...DEBUTED!
What I'm trying to say is that it's easy to get a little high on our own running abilities. Granted, the average jogger is in awe of how fast a real competitor can run. However, there are plenty of guys out there who can and do run respectable times off of a combination of talent and moderate cross-training volume.