I'm not sure how to count permutations in the 15 puzzle. They say that an odd count means it's impossible but not sure how to count this puzzle. How do I count whether this is even or odd? If it is solvable how can I solve? The last two tiles always seems to be swapped in the wrong position no matter how much I slide it around. I've been keeping the moves to the bottom half, do I need to do a big permutation around the whole puzzle?
Here's my grid results
| 1 | 2 | 3 | 4 | | 5 | 6 | 7 | 8 | | 9 | 10 | 11 | 15 | | 13 | 14 | 12 | |
Here's what I'm referencing