lag probably caused that

For some reason, if you're 15th or 16th for that matter, kill is a trooper or a tank it won't win the game. Your final kill must be a plan. Also, oddly enough if you're flying let's say Allied, and win a dogfight mission all Allied players in that mission get a win as well, even though there aren't any teams. I once lost a Dogfight mission with 18 kills because I was cleaning up tanks, and as they were respawinig someone else was getting the 13th, 14th and 15th kill on the other side of the map

Roy it may be due to lag as it may take time to register the kill.

It's kind of along the lines of what Ghost said. Don't quote me because I am not sure exactly how it works but from what I notice is that ALL chute kills that you get in a Dogfight mission do not get added to your total for the win even though the stats show it.

I had a game where it took me either 18 or 19 kills to win it and ever since that I kept an eye on how my totals accumulate. Tank kills DO COUNT from what I can see. I am not sure if the game can be won on a tank kill as Ghost mentioned because I never came across that situation.

Tank and chute kills DO count usually, they just cant be your LAST kill, otherwise you still accumulate them until your last plane kill after 15.

yes my last kill number 16 was a chute but the 15th kill was a plane and 15 is the magic number

Oh.... Well, lag issue for sure then