Does your car have an oil service indicator?
my DD honda has the % meter for the oil and pops up a code when it needs service.. my car is mostly highway driven.. so far the code for an oil change and tire rotation has popped up every 10,000 miles. at 30k the code for an oil change, tire rotation and to replace cabin and engine air filters popped up.. works for me.. the car uses a semi synthetic oil..
jamies subaru the dealer said change it every 6,000 miles. not even sure if that car has a maintenance reminder..lol. i've never looked at the manual to see what subaru suggests but she is all stop and go so i'm fine with every 6,000 miles.. pretty sure that car gets full synthetic..