After upgrading from 14.4 to v0.15.1.beta2, I noticed that GPIO 14 and 15 could no longer be used. Looked in release note and saw a recommendation to assign in the USERMODS menu where 14 and 15 are assigned by default to unassigned. While doing this lets one to assign GPIO 14 and 15 in the LED CONFIG menu, once you save it and go back to the LED CONFIG menu, the previous GPIO entries for 14 and 15 are now blank!
Sort of solved the issue. After unassigning GPIO14 and 15 in the USERMOD MENU, reboot WLED and then you can save in LED CONFIG using GPIO 14 and 15. The only issue really left is that you should get a warning that the LED CONFIG SAVE will not work if GPIO 14 and 15 are assigned in LED CONFIG without rebooting once they are unassigned from USERMOD MENU