For runners in the 1:45 or greater HM time range I think a HM schedule is perfectly fine. If you can run a HM faster than 1:45 then I think a fast 15k course is closer to aerobic threshold, and I might want to do some intervals on top of regular work. For me, I would do the following weekly runs....
One run of up to 2 hrs easy, with some striders towards the end
One run of around 90 min with up to 40 min at my perceived threshold.
Several runs in the 60 min range easy
All remaining runs would be recovery and would be easy.
In the final 6 weeks before the race I might find a 5k race or two, to get a sense of my race pace. These would also serve as VO2 max work, or alternatively I might do a couple of time trials or some 800 meter intervals.