1. The problem asks for the product of 7 and 8 decreased by $x$, where $x=15$. 2. First, find the product of 7 and 8 using the multiplication formula: $$7 \times 8 = 56$$ 3. Then, decrease this product by $x$: $$56 - x$$ 4. Substitute $x=15$ into the expression: $$56 - 15 = 41$$ 5. Therefore, the final answer is 41.