Hey Velogirl,
That's a nice time for your commute. If I'm the Crazy Biker Man then you some be the Crazy Biker Girl. LOL The go fast is so much fun, isn't it.
What I do when I get to used to riding at a set speed is down shift and then spin like crazy for a mile. Then just shift back up and ride. Your legs will be wanting to go so they will spin faster after you shift back up. Also to get up to speed at the start of your ride spin like crazy for a mile then ride on. I run in 7th gear at 15 mph, thats a Cadence of 82, for the 1st mile. This will make me ride faster through my commute. And eat everything. LOL