Big Mama- you are quite right- running 1.5 miles, then walking a spell is a VERY good way to train, and even to race, if you are going to find that getting round is your main goal- I did it for my first, and was surprised to see how good a time you can get that way. Don't knock it, run/walk is a very sensible idea- stick to it for the long runs, at least until you are comfortably managing about 15 miles, and just do the shorter, faster ones as continuous running when you can.
pw is personal worse- kinda opposite to personal best,