15-Mile Training Suggestions?

Hi Folks, I have finally, after two years of procrastinating because of performance anxiety, signed on for Stage 4 of Chao's 8 Bridges swim. I am totally excited and realizing that, dang, this thing is CLOSE! The stage is 15 miles. Last summer, I did a 13.6 mile, but it was closer to the end of July so my summer training and open water time was maximized. I am thinking about changing up my training a bit and wondering about opinions. Last year, I would do at least one day of straight distance, bumping my yardage up to my longest swims at around 15 thousand+ yards in a session, with a break every 2500 just long enough to gulp down some liquid feeding. Other days were a combination of 3 Master's practices per week, and another long swim but not quite at that distance. I also run 4 days a week, most runs being between 9-11 miles. (Did I mention I am doing a 1/2 marathon 3 weeks after the swim? What is wrong with me??) This year, I am considering something new and having my long days in the pool be a series of 500s, with a 10-15 second break in between. I feel like that might be more advantageous in terms of having a few seconds to refocus, remind myself to keep my form, and perhaps might be me swimming smarter rather than just swimming long? For example, on this past Saturday, I did 16x500 on 7:30 and am considering bumping it up every week so I add a certain number of 500s. (Yes, I know the yardage needs to be longer than that. There's that pesky issue of actually wanting to see my kid and husband and, oh yes, work.) I'd love to hear your preferred techniques, keeping in mind that these have to be achievable by a mere mortal! Thanks!