GP15 on RPi Pico is fine as far as I can tell

[danpeirce]

line 23 of https://github.com/adafruit/Adafruit_Learning_System_Guides/blob/main/Pico_RP2040_Mech_Keyboard/code.py

list of pins to use (skipping GP15 on Pico because it's funky)

It looks to me by discussion at adafruit/circuitpython#4063 it should be okay to use GP15. While it is probably unnecessary to change the code perhaps the comment should be updated to state the issues with GP15 have been resolved and it can be used in new designs.
I'm raising the comment as an issue because one can spend significant time attempting to gain some understanding of "because it is funky" only to find it was a temporary issue years ago.
I'm thinking of adapting this code in my own project and so far as I read so far using GP15 would be fine. Note in my design I will not be using a PCB and will use point to point wiring. This looks to be straight forward when not using a matrix or diodes. I'll test when my hardware arrives.