I don't care how many kills you got.
Until Riot adds a win condition that is "When you have 30 more kills than your opponent you immediately win the game" you KDA means very little.
Next time you're like 5-0 as a zed against your mid-laner. Take his tower. Then roam bottom, with a gank that kills to people and TAKE THE TOWER
Then you roam top and get a nother double kill that kills the enemy jungler and their toplaner... TAKE THE GODDAMN TOWER.
Then when you push your enemy out of his lane TAKE YOUR SECOND TOWER.
Also... If you get a few kills on bot, TAKE DRAGON.
This game is won when you kill the nexus.
If you think 14/0/15 is akin to taking the nexus, you're horribly misguided.