I suspect folks will want to know: If you have never set your poles longer than 115, why are you considering the longer poles? Folks may ask if you ever find need for the shorter setting. Another question will be how steep the terrain is and what are the most challenging obstacles.
Absent answers to those questions, I would suggest the longer of the two options. Because on very steep uphills you can still shorten them a bit and the poles probably have an option to remove your hands from the straps and grab the handle a bit lower. By my way of thinking, steep downhills and “steps” or “ledges” are a higher risk and higher stess scenario and that scenario benefits from the option of longer poles.
I can tell you what I do. I use the fixed length Black Diamond Carbon Z poles – because they are “oh so light” and swing so nice (I was a collegiate Nordic ski racer and came to appreciate light poles and a nice swing…). I purchased my first set of BD poles at the long end of my range, and last year I purchased a second set at a more natural length. Personally, I find steep downhills and stepping off boulders, rocks, ledges and stairs to be more “risky” than climbing up. I’m pretty good at going uphill. So my “stress case” is going downhill. slightly longer poles are better for going downhill (steep downhills with ledges of some sort). But on a well travelled path with few tricky downward steps I prefer a traditional length because they “swing” better.
I also prefer to NOT using hiking poles if the trail has no challenges. But, I also have a so-so repaired ruptured achilles on one side, and a knee replacement on the other. Uphill still = no problem.