Answer
A decrease of $15^{\circ}$ Celsius is more than a decrease of $15^{\circ}$ Fahrenheit.
Work Step by Step
$F = \frac{9}{5}C+32$
We can use this formula to convert from Celsius to Fahrenheit. The factor of $\frac{9}{5}$ means that for every $1^{\circ}$ change in temperature on the Celsius scale, there is a $(\frac{9}{5})^{\circ}$ change in temperature on the Fahrenheit scale.
If the temperature decreases $15^{\circ}~C$, we can find the decrease on the Fahrenheit scale.
$(\frac{9}{5})~(15^{\circ}) = 27^{\circ}~F$
This is more than a decrease of $15^{\circ}~F$.
Therefore, a decrease of $15^{\circ}$ Celsius is more than a decrease of $15^{\circ}$ Fahrenheit.