Hello,
after some time wondering whether I should suggest it or not, I have decided to do it:
A short introduction to the game:
The 15 Puzzle consists of 15 squares numbered from 1 to 15 that are placed in a 4 by 4 box with one empty position. The objective of the puzzle is to reposition the squares by sliding them one at a time into a configuration with the numbers in order.
I was not sure whether to post this or not because I have read that there are some cases where, even if the numbers are randomized, the puzzle can't be solved, so I made a research about how to find out when it is solvable or not, hoping this helps, here is the link with the info:
https://www.geeksforgeeks.org/check-instance-15-puzzle-solvable/
My suggestion is it being added to the arcade games, and the global scores could depend on the time someone took to solve the puzzle.
I hope you consider to add it in a near future.
Kind regards,
Diana.

Hi. Very good suggestion.
If you start from a solved position and randomly slide blocks creating a messy position, you are sure to be in a position which is solveable. Of course, I think there might be good algorithms to randomly generate a solveable position. But I suggested what came to my mind just to show that it is not a big hindrance.