i found an old crank that happened to be 165, i've used it for commuting /long distance rides/ low gear spinning, i race single speed CX and i was definitely considering running with the same crank arm length. IDK if 5 mm will make the difference, but i think it could be worthwhile.......on the flip side, i know guys out west who run 175, it's all a crap shoot sometimes....go with the lightest and strongest in your price range
I think it's fine to experiment, certainly. That's not a big difference. On the other hand, if you find 170's uncomfortable I'm not sure simply shorter cranks are going to address the issue. But it's a small experiment so it's worth trying.
You won't really have any change in leverage. It's a geared bike and the difference is so small it won't have much effect.