Arrange integers 1- 15 in a triangle such that the upper row consists of 5 integers, all other rows represent each the absolute values of the differences between the adjacent members of the row above so that the 5th row contains one number only.

A bad example:

4   7  15  10   2
  3  12   5   8
    9   7   * oops!  Can't use 3 again.

Just wanted to explain the build-up..
Better luck to the solvers!