WHOA! Sounds like you are planning on training for Dopey then. An 18 month time-frame....
LOL, I'm reading this and thinking well it would be nice to know her goals, and then bam you already knew what I was going to say. Looks like we're on the same wavelength.
That seems very reasonable. Looks like you were running around 60-70 miles per month before the 15k. So dropping down to 48.6 miles will definitely maintain those fitness gains. I would focus on lots of easy mileage this month. It will allow you to recover from the 15k, maintain fitness, and prepare yourself for the rigors of half-marathon training.
As for training paces, the choice is yours. Based on how the 15k went, I wouldn't change the training paces from the last cycle. Although I do remember you ran another race, was it a 5k? Did you beat the 27:57 predicted time? By all means if you want to run a 5k in late December (and it doesn't have to be official, but preferably outside), go for it. It will likely give us a better place to start then using a 15k from Nov or a 5k from further back. But don't be discouraged if you don't beat the 27:57 (or your 5k PR) because you won't have been in serious training mode so you may not have what it takes to hit it again (you could or could not). Don't take it as a negative though regardless.