Two Point Campus

Where is Cheeseball?
You unlock Cheeseball in Fluffborough, the #6 campus. (Right after getting one star on Campus #4, I was able to skip Campus #5 and go right here.)

What is Cheeseball?
Fluffborough is a Sporty campus, and Cheeseball is their main sport. It involves 2 teams of 3 players throwing wheels of cheese into graters.

How do I get 15 wins?
Build your Cheese Course (sportsball stadium) and click on it to choose Create New Event. This lets you challenge an opponent's team. Cheeseball competitions need to be planned ahead of time, and take 2 slots (1 month) on the schedule. You need to have 2 free spaces where classes are not planned.

Your players are just like normal students. You want to make them happy, going to class, getting tutored, give them food, dorms, clubs, and entertainment. You can also build a gym which I think helps.

Also I'm pretty sure you always lose the first game you play, against Jumbo Mega Team, just, so the tutorial can tell you to build a marketing department.

But what's the Easiest Way to do this?
I found an easy way to cheese (cheeseball?) this achievement.

You could set up 15 games, wait for them to happen, possibly lose some of them. If you're only playing 2 or 3 games a year, this could take 5 or 6 in-game years.

Or you could just play the same game 15 times. The counter adds up after each victory, so exiting out and back in doesn't remove from the counter. In my second year I was challenged by the Smogley Salamanders. My year 2 students were at level 9 and won the game 3:0.

So 2/3rds of the way through the game, save and exit to menu. Then reload, win the game, exit, DON'T SAVE, and reload. Repeat 14 times and you should be good.

Also you win 2 K coins every round, so 30 free K coins.