This 15 device limit is separate from the pdcurses fuckup having to do with the cmd prompt window size?
15 devices, cgminer 2.4.1, window size 120x50: crash on startup
15 devices, cgminer 2.3.6, window size 120x50: works fine
EDIT: I've just had another Single go into the 'OFF' state (cgminer 2.4.2). That clinches it; I'm rolling back to 2.3.6.