To find the volume of a right rectangular prism, you can use the formula:
\[ \text{Volume} = \text{Base Area} \times \text{Height} \]
In this case, the base area is given as 15 square inches, and the height is 5 inches. Therefore, the volume will be:
\[ \text{Volume} = 15 , \text{in}^2 \times 5 , \text{in} = 75 , \text{in}^3 \]
So the volume of the gift box is 75 cubic inches.