The force that the hammer exerts on the hot metal is given by:
Initial momentum is 1500v
Final momentum is 0.
Where dv/dt is acceleration, being negative here.
So, net force = mg + F = 15 000 + 1 250 = 17 250 N
Maybe there's a typo in the answer you gave? Or if it's to the nearest 500 N, then it becomes 17 500 N