welcome along fella
Picking up a new ride can be daunting for just about anyone who is new to biking world. Like preunit has mentioned, pick up the bike after the rush hour either mid morning or mid afternoon, 15 miles isn't that far, but i do understand how you feel . You say you don't drive, do you not know someone with a small van ?, if not have you a mate who also rides, some one who can ride behind you in a dominate position in the road, so that you ( in front ) is as protected as possible from all the numpty arse london,,,," my journey is more importent than yours",,,, drivers. Word of advice do try to relax, and dont worry so much, you have your CBT which means that someone has said that you are competent enough to be on the road, and you should be filled with pride and excitement and at your age, your no chav, scooter riding knob head, with less concentration span of goldfish, honest mate you will do just fine, relax relax, relax & enjoy
Maybe you could share with us what area you live in and where abouts in london your picking it up from, you never know, one of us kind souls could assist ?