15. A.

From the problem, we know that the radius of the large dough circle is 3 inches. Therefore, the radius of the cookie made from the leftover dough is
$$
\sqrt{\frac{3^{2} \pi - 7 \pi \times 1^{2}}{\pi}} = \sqrt{2} .
$$
15. As shown in Figure 3, seven small circular cookies with a radius of 1 inch are cut from a circular dough. Adjacent small cookies are externally tangent to each other, and all small cookies are internally tangent to the dough. The remaining dough is reshaped into a circular cookie of the same thickness.

Figure 3 Then the radius of the circular cookie made from the leftover dough is ( ) inches.
(A) $\sqrt{2}$
(B) 1.5
(C) $\sqrt{\pi}$
(D) $\sqrt{2 \pi}$
(E) $\pi$