So I am going to sign up for a 15 mile race 7 months from now. The entire race is at high altitude and a lots of elevation gain. I've only done 5ks before and I always have a lot of trouble with hills. I'm wondering what level of training I'm going to need to do to get better at hills, trails, and altitude. So far my road record for distance is 6mi and my trail record is 4mi.
Am I making a mistake or not (I'm doing this either way)?
It's doable in that amount of time. Make a training plan, but don't be so rigid with that plan that you get an injury. Listen to your body.
I'm not an expert but I have been running for a long time. I'd start with low heart rate training. Do mostly slow runs, gradually increasing your mileage until you get to the target mileage. You want to be doing 80% of your mileage in zone 2(if you don't use any technology, zone 2 is about where you can easily say a few sentences while running). Once you're comfortable at your goal distance start phasing in speed work and more hills.