the pace for this ride isn't fast - actually you can go whatever speed you want and there will be plenty of people going slower. don't worry about being competitive. there are also a lot of areas to stop, so if you get tired, just rest for a little.
being a new rider, your first goal is to get the bike out and ride. at least a couple of times a week...maybe take a longer ride on the weekend. start slow and ramp up the miles by adding a little more each week. the biggest problem most new riders experience when they go out for a long ride are all the little aches and pains from sitting in the saddle so long. you'll probably be on the bike for a good 4 hours or longer. the sooner you get your body used to riding the better. I would try to work up to a 30 mile ride or longer by the time you try this.