Absolutely make a few test runs. Give yourself enough time cause you might get flats or something like that. Your average speed is not the speed that you can hammer for 15 minutes. It depends on traffic, signals, your fatigue etc. Also make sure you have comfortable clothes to bike, and clothes to change into at work !! (Don't forget an extra pair of underwears and socks !!!)

Try to look for the best possible route which means not the shortest route, but the most bike friendly route with a low speed limit ...

14 miles is not a short distance. It depends on what type of shape you are in. If you are in a decent shape, you can try going for it may be 2-3 days a week. See how you feel, and work your way up.

O and did I forget to mention that - congratulations on giving bike commuting a thought !!!! Once you start it, you will get hooked to it !!

HTH