On the heart rate, explain how to get it back down and what a dangerous level is if that's possible. My heart rate gradually climbed the entire race peaking at 186 as I was attempting to sprint the finish.
That's a lot for a 15k in cooler temps. That's usually 5k territory. You were redlining.
You just need to slow down for a second and let it cool down. Losing lbs also helps. Puts heart and muscles under less load. Best thing of all is to simply condition it. Having a low resting one and high possible threshold is a good sign of a solid vo2 measure.
Have you figured out your hr zones yet with an LT test?