I put on about 70 miles per day on my 17 Corolla, decent amount highway speeds. I split the difference at 7500 - 8000 miles. Which, basically, ends up being before summer and before winter. At 85k miles and doesn't burn a drop. If I only drove around town I'd probably drop to 5k/6mths because I'd consider that "severe", personally.On the newer Toyotas oil changes under warranty are done at the 10K mark. Is this ok?
So, really, as others said, depends on your driving habits and how you sleep at night. Read the owner's manual and see if you can into regular or severe. If you still struggle to sleep, do a UOA every change...