To solve for this we need to use the formula P = W/T (Power = Work/Time).
Since we do not have time, we shall switch up the formula.
Our new formula is T = W/P (Time = Work/Power).
We have 1,800,000 J of work, and 15,000 W of power.
1,800,000/15,000 = 120.
It will take 120 (insert measure of time here).
I hope this helps!