15. Given
$$
3^{p}+3^{4}=90,2^{r}+44=76,5^{3}+6^{3}=1421 \text {. }
$$

Then $p r s=(\quad)$.
(A) 27
(B) 40
(C) 50
(D) 70
(E) 90
15. B. From the known information, we get $p=2, r=5, s=4$. Therefore, prs $=40$.