15. As shown in the figure, line segments $A E$ and $F G$ divide rectangle $A B C D$ into four parts; the areas of two of these parts are 2 square centimeters and 11 square centimeters, respectively, and $E$ is the midpoint of $B C$, $O$ is the midpoint of $A E$. Therefore, the area of rectangle $A B C D$ is $\qquad$ square centimeters.
Answer: 28