Hi Timothy! You should totally do the half marathon!
If you are already a fast walker, then you will be fine. The 16 minute/mile pace starts when the last person crosses the starting line. So positioning yourself in a higher corral, or even at the start of the last corral would give you an additional amount of time to finish in. There are a very large number of walkers in the Disney half marathons.
I prefer the run/walk/run method that the runDisney trainer,
Jeff Galloway, recommends. I will run for 3-4 minutes and then walk 1 minute. I do this for the entire race, and it has made a huge difference in the way I view running. I think you would be surprised at how much you can jog/walk by using this method.
However, if you did sign up yet didn't finish, you would still be awarded a medal. All starters will receive a medal at runDisney. But, I just know that you can do it! Let me know if I can help you in any other way as you plan and train for the race!