i have a 2015 corolla ,how often do i have to change the oil ,i had my last oil change 6 mo. ago ,but only put 3000 miles on it since then,the dealer said i have to wait until i have 10,000 miles or 1 yr..I don't put many miles on ,just to show this car is 18 mo. old and i have only 7000 miles on it.I guess i'm from the old school of changing oil every 3000 miles.i'm 80 yrs old and don't drive much ,just short trips to the store.Just not used to synthetic oil,but i guess this normal?