There's not a huge difference in preparedness between -15Fand +15F.

It's (literally) just a matter of degrees (bah dum ching!)

But in all seriousness...

You'll go through heating oil faster. If you park your car outside, it might be hard to start if the battery is old. If your cars are parked outdoors, you might want to add some fuel line antifreeze to the fuel tanks. It's basically just isopropyl alcohol. If there's any water in the tank, fuel filter, or lines, it'll prevent it from freezing.