I mean that your 1500m time is a fair bit better than your 5000m time. That's pretty common if you're young.
As for long runs, that depends what else you want to run as well as 3000s. If 3000 is the longest you race, there's probably not much point regularly going over 10 miles, but I've never trained specifically for that distance, so not entirely sure.
At the risk of looking like I'm talking to myself like the bearded weirdo in the wee-stained trousers at the bus stop, I was thinking more about what difference raw speed would have made. Last night, I overtook a young bloke at 400m to go who seemed to be struggling. He came past again at 250m to go and finished with enough aplomb that he ran 9:02 to my 9:08. 6 seconds in 250m! And I finished OK by my own poor standards, even managing the rare feat of taking a place in the home straight. If I had the kind of raw speed he has, I'd have easily broken 9 at least twice last year purely from the finish alone.
There are those of course who say that the finishing speed isn't about raw speed at all, it's mainly down to whoever has the best aerobic endurance so they've got something left from the race. These people are largely wrong. I've been easily beaten in a fast finish in cross country races by enough youthful middle-distance specialists who theoretically have far worse aerobic endurance than I do to know that's the case. I could have jogged 6 and a half laps at 8mm pace last night and I still wouldn't have finished like that.
In an even stranger addendum, I just went out and did some reps in the park. Not ideal doing them the morning after a race, but I have no other chance this week. Track wasn't available so I was working off the 100m markers set into the path. Aimed for 6 x 1200, and my legs managed to muster 5 x 1200 in 3:36, 3:37, 3:38, 3:37, 3:36, and then did 4 x 200 in 33s as I couldn't face a final 1200. Don't ask me to square running a 9:08 3000 one evening, and then doing 5 x 1200 at a faster pace the very next morning, as I can't work it out either. I'm willing to accept that the 100m markers in the park might not be 100% spot on, but I can still compare it to plenty of previous rep sessions using the same markers, and it compares very favourably. Mysterious.