Thanks for the kind words! Glad you had fun with the game!
I did the level design for level 15, and I believe you caught a flaw in that design. In previous iterations of the game, the limited-use arrows didn't count down if a robot passed over them that was already heading in the direction the robot was heading. So, it only counted down if the arrow actually turned the robot.
I thought that was inconsistent, so I made the recommendation that the limited-use arrows countdown whenever a robot passes over them, regardless of whether the robot was actually turned.
Unfortunately, I didn't realize that the solution for that puzzle was benefiting from the previous version of how the arrows functioned, and so that solution no longer worked.
I'll make an update for that puzzle, and we'll update the game once voting is over.
So, well done on completing the game, even my broken puzzle!
Thanks again for the feedback, and we're glad you enjoyed the game!