(15 mg psilocybin / 1 kg body weight) * 80 kg body weight = 1200 mg psilocybin
1200 mg psilocybin * (1 g psilocybin / 100 g dried mushrooms) = 12 g dried mushrooms
I think it’s 12 grams dried mushrooms, which is almost half an ounce, like you first said.