I want to find the relationship between the temperature change and the time elapsed. I can use a proportion to compare the given situation and the unknown situation. Let $x$ be the temperature change in $2$ hours. Then I have $\frac{1.5}{15} = \frac{x}{120}$, where I converted $2$ hours to $120$ minutes. To solve for $x$, I can cross-multiply and get $15x = 180$. Dividing both sides by $15$, I get $x = 12$. So the temperature will rise $12$ degrees in the next $2$ hours. 
The temperature in a desert rose $1.5$ degrees in $15$ minutes.  If this rate of increase remains constant, how many degrees will the temperature rise in the next $2$ hours?