Same as any PC - 15
A long time ago some Geeky post-billionnaire thought 'Who will need to connect more than 15 things to a PC... and it's stuck. Things like IRQ Steering make life easier for us, but regardless of CPU - The system architecture of the PC dictates 15 IRQ's and some are reserved like IRQ2 for (IIRC) system clock etc.
IRQ's are best ignored unless you're getting conflicts.
hth