How much work is done in moving a load 15 meters using a force of 15 newton’s

225 joules.

Explanation:

If this a one dimension problem, this is the motion is in the same direction of the force, the equation for work is:
Work = distance × force
⇒ Work = 15 m × 15 N = 225 joules.
This is a special case of the general equation 

Work = |F| |displacement| cosine (angle between the force and displacement)

When force and displacement are in the same direction, the angle is 0, so cos(0) = 1. This is the two vectors are parellel and the work is just the product of the two magnitudes (force and distance)