Like you suggested, try the ride out and see how long it takes you and if you are comfortable with it. My commute is 10 miles, but I am lucky in that nearly the entire ride is on paved trails, I have no hills, and I can shower at work. If it is too long or strenuous with the hills my suggestion, if possible, would be to drive a bit closer until the distance becomes manageable. You can always increase the distance when you feel the need. Last year due to flooding I had to take an alternate route and decrease my distance to 6.5 miles, but the important thing is I was still on my bike.