If you can run 15 miles at a training pace of about 7:40 per mile, your goal requires a pace almost 45 seconds slower. It should feel like a long training run for most of the time. The big question is "what happens when you run out of gas?" or, more technically, when you become glycogen deprived. You likely haven't been in that space before so the mental effort may be a challenge, but that depends on your other activities and overall fitness.
As for the pace groups, I suspect you would find that having them gradually pull away from you only to come back in the walking portion, repeated 20+ times, is very frustrating. If you're comfortable doing the limited mental math, use your own watch to time yourself and don't worry about the pace group. They are great for those new to the event, or those who are seeking a particular time, but you either need to practice the 10 & 1's or find a pace group doing a continuous run.
Don't forget that tapering really does matter, and save the partying until the run is done. These are standard recommendations but they do make a difference for most of us. Have fun.
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