This is a semi educated guess, I am not knowledgable about electricity.
Let E= k/d and C=md whee k and m are constants. (but we do not need to worry about C.)
and d is the distance between the chages.
Initially
kd+kd+kd=3kd=15J
Now move the charge and the distances become d/2, d/2 and d
so new energy is
kd/2+kd/2+kd=5kd=15∗5/3Joules=25J
So if my reasoning is correct there will be 10 more Joules of energy.