The overall liquid amount is like 9 - 10 ml, of which ~1.5 ml is whisky. That’s still not little, but it’s more like 6 % abv, so far from the 15 you calculated. But I agree that even that is probably a tad much. On the other hand, if I want to use it in a co-fermentation or even staggered pitch, it has to be able to take a punch.