5. Let positive integers $a, b$ be less than 6. Then the minimum possible value of $2a - ab$ is ( ).
(A) -20
(B) -15
(C) -10
(D) 0
(E) 2
5. B.

From the problem, we know that $a=1,2,3,4,5 ; b=1,2,3,4,5$. Therefore, $2a-ab=a(2-b) \geqslant 5(2-5)=-15$. At this point, $a=b=5$.