It's all very well having a major goal, e.g. to lose 5 stone, but you need some intermediate targets that are not too difficult to achieve and allow you to make regular progress. You have a 15 mile journey to and from work. If you can cycle in one day, leave your bike and cycle home one other day, then get out for an hour or two over the week-end you'll have a good base to work on. Finding a club or group to get out with at the week-end would be a big help.
At the end of the day, though, you've got to want to do it. The hardest part is always getting the gear on and getting out of the door and onto the bike. Once you're on the bike, finishing a run is the easy bit.