If you make it to level 15 in rumble pit then you start to get your ass handed to you and you are falling middle to bottom of the pack everygame, why would you want to drop down levels? If your K/D ratio is anywhere between -2 to +2 then you are right where you belong. You should stay at that level until you get better, then you will start to level up.
You earned that 15 in rumble pit, why do you want to lose it so quickly?
In order for a ranking system to work (and by work I mean largely to stop assholes from de-ranking) some people have to get bit in the ass. If the small percentage of people get bit in the ass and it stops most of de-levelers then the SYSTEM WORKS