Just had mine done at 7500. I asked the dealer to give me the old plugs back (I gave him the new plugs as I got them cheap). I stood in the shop and held one up and said, "nothing wrong with these, why does Suzuki insist they get changed?". Dealer agreed they were fine, said he just follows what's in the service book (fair enough).
Bottom line is these iridium plugs should be good for waaaaay longer, so don't feel bad about not changing them every 7500.