If it's that hard to path I'd knock that one out as a through run and make it a Barrow. It presently sits there 10 minutes which is bad enough, but this is useless - presumably the extra 20ish from the time gained by running via Bolton.
If you did that, you wouldn't have any through services between Windermere and Manchester at all, because they're
all like that!
In the first pair, the 0829 waits 13 minutes at Preston and a further 2 minutes before Oxenholme Lake District. The 0955 from Windermere waits 17 minutes at Lancaster.
In the second pair, the 1129 from Manchester Airport waits 10 minutes at Preston and 12 minutes outside Oxenholme Lake District. The 1307 from Windermere gets incredibly lucky and only waits 5 minutes at Lancaster and 3 minutes at Preston.
The next pair we've just described.
For the final pair, the 1729 from Manchester Airport waits 9 minutes at Preston and 2 minutes outside Oxenholme Lake District. The 1856 from Windermere waits at Preston for 17 minutes.
The extra 15-20 minutes sitting around on nearly all services isn't because time has been saved running via Bolton either, it's between timings between Manchester Airport and Preston which have been agreed cross-industry as part of the Taskforce are simply never going to marry up perfectly with the very few slots between Lancaster and Oxenholme Lake District to which Northern have rights. Northern have next to no chance of more or better slots on this section because of Avanti West Coast and TransPennine Express blocking paths while failing to actually run the trains in them, and more importantly the interests of the FOCs. The fact that the branch is one train working and there's not a second platform at Oxenholme Lake District which can access it also means that only a perfect exchange is possible i.e. the two services need to be passing each other 2 minutes south of Oxenholme Lake District. This is simply never going to be possible with the through running beyond Preston.
Abandoning through running to Windermere is something I've been in favour of for quite some time, though. It might be possible to have more through between Preston and Windermere ar half decent journey times, plus of course the first one to Windermere and the last one from Windermere are actually quick. I have made it no secret that if it were up to me I would have an hourly Manchester Airport - Lancaster EMU and hourly Preston - Barrow-in-Furness DMU. Windermere - Lancaster services could then run ad-hoc.