I enjoyed reading your post. I feel you with that sub 16 minute goal.
Last year I was aiming for under 16 too but sadly the rest of the guys were in the 14:40 and 15:15 range so going with 70 second laps would have been suicidal.
I decided to aim for 77 second laps, which would be like 16:02 pace and hammer the final lap.
It virtually came down to a time trial for me, and last week I was able to run a 12: 53 4km (16:07 pace) in training with 2km worth of drafting and still negative spliting (6:29 and 6:24) + a 1km repeat of 2:56 with the last 200m in 32 seconds (the reason I was sure I could hammer the last lap for the remaining 2 seconds).
First 3 laps were manageable even running alone, but then I started running 78 seconds (that 1+ second would eventually pile up and screw the goal).
So 3:12 + 3:15 + 3:15 for a 9:42 3km and it was evident that the sub 16 wasn't going to happen that day. A next 3:17 km eventually cleared any doubt that could still exist.
I still remember watching at my clock at the bell and seeing 14:58. I wanted at least 12 seconds faster. Still I ran a 75 last lap (which i swear it felt like a 66 second lap), which gave me my 16:12 pr.
However I'm pretty positive that this year I'm going to be able to run 15:3x (even alone if I focus enough) I'm still 21 years old.