It’s up to application software to define what it does. I have never seen a keyboard with function keys beyond F12 in person, but they do exist. Software is very unlikely to respond to F15, which is why Caffeine uses it to keep the system awake. Notably, the program can also instruct Windows to stay awake using its native mechanism instead (possibly insufficient for something like MS Teams) or another virtual key code of the user’s specification.
It’s up to application software to define what it does. I have never seen a keyboard with function keys beyond F12 in person, but they do exist. Software is very unlikely to respond to F15, which is why Caffeine uses it to keep the system awake. Notably, the program can also instruct Windows to stay awake using its native mechanism instead (possibly insufficient for something like MS Teams) or another virtual key code of the user’s specification.