Toyota Repair: Sparkplugs, resistor type, manual toyota

Question
How can I tell if my tacoma pre runner has regular or Irridium spark plugs?(v-6 DOHC 24V enginew/WT-i

It was built in March of 06 and the new owners manual toyota sent me for 06 says I do have the better plug?

Dealer wanted me to tune up vechicle at 15,000 service, I did not get tune-up felt it was to early even if it has reg sparkplugs.

Answer
It has regular resistor type spark plugs which should be replaced at 30,000 miles, by the way there is no such thing as a "tune up" anymore for late models, except for replacing the spark plugs,air filter and regular oil changes the engine needs nothing else. A 15,000 mile service should include an oil/filter change, air filter, rotate the tires and inspect and adjust the brakes and just a visual inspection of everything else, nothing else needs to be  done at that time.