I have a Toyota Sienna 2004 model, which I bought in 2004. The tires were rotated at 15K miles during a maintenance service about a yearago. Now, all 4 tires are completely worn out especially the edges after a total mileage of < 27K miles in less than 3 years. The mileage is about 75% city miles (35-50 mph). Is it normal to have tires worn out so early?