Averaging 15mph over that distance, over that terrain, with those breaks with 4 1/2 months to get up to it....no, you won't be able to achieve this brief in the timescale.
Not wanting to be negative, but you want to do some training to build up to it, come out with me on a saturday or sunday (I'm in Cheltenham), and you will see the difference between what you are hoping to achieve, and what you can actually do in a few hours, and then see how you feel afterwards.
I'd not attempt it in that timescale, and my normal ride is up to seven springs. It is something you would need a couple of years to build up to...as well as having little else in your life to occupy your days.