I've been using the 50 litre One Planet 'Overshadow' for the past ~3 years. It is essentially the predecessor to the 'Canopy' and virtually identical as far as I can tell.
I love the pack, and am only
trying to sell it here because I have found that I occasionally need it to be just a tiny bit larger than that, and because I prefer larger pockets (the Overshadow/Canopy front pocket is just a sheet of stretch mesh and the top pocket is a tad smaller than I like).
The fabric is not as abrasion resistant as their canvas packs (I also use an old canvas One Planet Strezlecki). But if you're not pack-hauling or dragging it over rocks, it should be fine. After about 3 years, my pack still looks like its in near-new condition.
I've not tested the waterproofness of it in any river crossings, but I've not come across any pack that is truly waterproof (as in hold in under water while crossing a river for a few minutes always lets a few drops in). I've used in it moderate rain without any trouble, but I would always keep clothes, etc, in their own dry bag inside the pack, anyhow.
Yes, 15kg is fine in the Overshadow. I'm not a light-weight walker, and I've used mine for a 4 day walk, including carrying a pack raft and paddles. I don't weigh my packs before walking, but I would GUESS that it would have been at least 15 kg on that one.