Elevator 1 moved up 15 feet from the ground level. its position is labeled as +15. elevator 2 moved down 6 feet from the ground level. its position is labeled as (use the hyphen for negative such as -1)

The ground level is to be the zero level. When the elevator moves above the ground level, it is moving towards the positive integer and when the elevator moves below the ground level, it is moving towards the negative integer. 

Elevator 2 moved down 6 feet from the ground level hence its position is labelled as 

Magic man is here, but unfortunately he is broke won’t you him out