15 (Fifteen) is a sequential movement puzzle made up of 15 consecutively numbered sliding blocks, all placed in a square tray large enough to hold 16 blocks. After the pieces are scrambled, the solver has to restore the blocks to the original order. You may make the game easier by lowering the number of blocks to 8 (3X3) or make the game more challenging by increasing the number of blocks to 24 (5X5). You may also insert a picture into the puzzle. This sliding-piece puzzle is a real challenge, so put your brain to work and prove how smart you really are.