How exactly kodular takes commissions?


I have always wondered how exactly Kodular takes commissions from our ads? I know its something like postback. So with Fenix update, they take 15%, right? But 15% of what? Total earnings for the month, for the day?
Or does they take 15% from each ad placement we have. For example we add 2 Interstitial Ad placements, showing fullscreen ads in different places of the app… do they take 15% of each placement , making it total of 30% from both interstitial placements, or they take 15% of the total impressions we receive per day/week/month? What if we add like 1 placement for InterstitialAds, generating all fullscreen ads in app. Will they only take 15% ?
I am just curious how it works

They calculates % on the total number of ads shown on app. Lets say, your app shown 50 ads last hour. So, there will be 8 ads from kodular and the other 42 ads were from your ad account.