half marathon training question

Hey BTers, I'm planning my first 15K on March 26, 2006. I'm also thinking about a half marathon on May 7, 2006. So, that gives me about 6 weeks between the two races. I’m planning on a slow build to the 15K (following Hal’s plan, with an extra week thrown in, plus I will be working on my running base all winter).  Here's a tentative plan for the long runs (comes mostly from Hal's half mary plan):

What do you think, are the two races doable?

Also, Hal Higdon's half marathon plan has you running 10 miles as the long run the week before the race. And then running 13 miles the next week. Am I going to be able to run that additional 3 miles without training, and without injury? I've heard that you never run the full distance, but after getting a stress fracture last year b/c of increasing my mileage too quickly, I'm a little paranoid about that extra distance (esp. since this would be coming into tri race season). That's why I put the 11 mile day in before the 1/2 mary, but that still leaves 2 miles.....