There really aren't a lot of 32mm knobby tire options out there, and for a 15% loose surface climb I would definitely want some tread, and as wide a tire as would fit.
32mm Gravel Kings are probably a top choice. If you can squeeze in 33mm, there's a bunch of CX specific tires out there that might work. Two of my favorites:
https://www.challengetires.com/shop/...s/dune-2/55047
https://www.donnellycycling.com/coll...ready-clincher
35mm Conti Terra speeds seem to measure a bit small on some rims, so they might be an option if you can squeeze them in.