Plenty of people commute 15 miles each way. Mine is 12 miles each way which is no problem. If you are healthy and in good shape a 15 mile commute should not be a problem due to the distance.

Depending on what you have now you may want a different bike. You'll be getting home later and leaving earlier which could be a problem depending on your situation. (I know my wife wouldn't like it if I told here I would be home 20 minutes later every day)

Paul