FWIW Canon 15-85 is an excellent lens even compared to modern lenses, it's one of my favorites.
A surprisingly good lens is Canon 18-55f3.5-5.6 IS STM !!!!! a very decent performer with a tiny size and while being very affordable
Psst, pretty much all 18-55mm are good ;-)
Chief Editor - opticallimits.com
Doing all things Canon, MFT, Sony and Fuji
750D plus 18-55 is an awesome combo for hiking, lightweight and very decent image quality, you don't need f2.8 and faster for such trips. that's why I keep 7D2 and EOSRP at home and use it, when I am not in group and I can take my time and do some birding it's 7D2 that I prefer though
Although both are good performers, I would still prefer a small SLR, it has better grip in my hands, 100 grams weight gain easily compensated with extra batteries I have to carry with me, in sunlight the EVF is better and no need to turn camera on and off to save batteries.
I did try Sony A6000 and EOSRP for hiking and I still prefer SLR, at least for me the major advantage for mirrorless is eye autofocus and focus precision plus very adequate metering for portraiture, I need none of them for hiking