Stray IRQs are indications of hardware IRQ glitches, mostly from hardware that removes its interrupt request in the middle of the interrupt request acknowledge cycle.
One has three options for dealing with this:
Live with the warnings. All except the first 5 per irq are suppressed anyway.
Break the warnings by changing 5 to 0 in isa_strayintr() so that all the warnings are suppressed.
Break the warnings by installing parallel port hardware that uses irq 7 and the PPP driver for it (this happens on most systems), and install an ide drive or other hardware that uses irq 15 and a suitable driver for it.