Notes on this puzzle
This medium slider scatters 15 tiles across a 4×4 tray, with the gap in row 3, column 3. 3 tiles start in their home squares.
Add up how far each tile is from its home square and you get 18, so no solution can be shorter than 18 moves. The shortest possible solution is exactly 18 moves. Matching it is a real achievement. Solving it row by row, the method from our guide, takes 64 moves on this board. Tile 6 has the longest trip home: 3 squares.
Where to beginTiles are not far from home after this short shuffle; fix one corner, then grow outwards from it.