Which is more work, pushing with 115 N over 15m or lifting 20N over 10 m?

Work = (force) x (distance)

You could look at the two cases, and see right away that

the first one has more force acting through more distance,

so it must be more work. But since I just gave you the formula

for Work, let's calculate the amount of it for both cases:

First case: Work = (115 N) x (15 m) = 1,725 joules

Second case: Work = (20 N) x (10 m) = 200 joules

The first case involves 8.625 times as much work as the second case.

Work is simply the force applied over a distance.

Work = Force * Displacement (m) ... In some cases where an angle is involved cosФ (theta) is used

Work = F * D (m) * Cos (an angle measure)

So for lifting the object cos (90°) would be used ... while pushing cos (0°)

When you work out the formula for each it should be clear what the correct answer is.