For San Francisco, 35mpg with a 15 mile commute is not bad. You will see noticeably better mileage when you take trips in the 20 to 30 mile range. Here are a few things that can help you get better mileage:

Look ahead and try to avoid using the brakes, instead coast to slow down when possible. On down hill sections, ride the brakes to slow down gradually instead of stopping all at once at the next light or traffic jam.

Accelerate at a reasonable rate past your target speed by a few mph. Then back off the gas until you can hold 45 to 55mpg on the mpg gauge. Going up hill, get moving, then back off and maintain your speed. Slowly accelerating up a hill kills mileage. So does speed. Avoid going over 70mph, and keep it between 60 and 65 on highways when safe for best mileage.

Mileage will improve if you air up the tires to 40psi, use ECO mode, avoid A/C or defroster usage, and avoid slow acceleration.

Force full hybrid mode by stopping while the warmed up ICE is running (tap the gas to force the ICE to start if needed) and letting the ICE stop after 7-10 seconds. Once in full hybrid mode, the ICE will almost always stop anytime you coast or slow down from any speed under 40mph.