I recently bought a 2015 Toyota highlander with 156k on the clock. It ran OK, but I pulled a couple plugs in the left bank to see if they had been replaced in the past. NOPE, the factory installed NGK Iridium plugs were still in there...
The center electrode was worn about .004, but for the mileage was amazingly intact. It does run better, with improved throttle response and power.
Getting at the plugs on the right bank required removing the entire intake system and gymnastics to reach under the cowl...
GGRRRR...