I don’t think of myself as a strong walker, more a maybe slightly above average walker! We walked the Pennine Way over 20 days but that included a short 6 mile day to Malham and a rest day in Alston. So I would think you could probably easily do it in 15/16 days. The miles do seem to get easier the further you go as you get used to it. I was surprised that I managed Dufton to Alston better than I thought.
Sleightholme Moor - I tried to persuade hubby that the road would be a better bet but he wasn’t having it! We had to stick to the official route. Actually it wasn’t too bad, as it hadn’t rained too much before then, it was further north when the bogs were worse - Padon Hill, and yes we had to do that too, not take the forest road!