1. The problem asks to write the fraction $\frac{15}{5}$ as a whole number. 2. Recall that a fraction $\frac{a}{b}$ can be written as a whole number if $a$ is divisible by $b$. 3. Here, $a=15$ and $b=5$. Since 15 is divisible by 5, we can divide 15 by 5. 4. Perform the division: $$\frac{15}{5} = 15 \div 5 = 3$$ 5. Therefore, the fraction $\frac{15}{5}$ as a whole number is 3.