15 is pretty much the recommended level to start the Expedition content, but there's some wiggle room. It sounds like you're new to UnderRail, so going at 15 is going to be a little tough.
Crabs are not easy. They're not the harderst things you'll find in the Black Sea, but that area you're in is sort of a harsh introduction. If you don't have a lot of W2C bullets on you, you may want to go back to either the expedition base camp, or even Core City, and stock up. W2C will be a big help against those crabs.
Also, yeah, a good crafted weapon will be leaps and bounds better than whatever you can find or buy. If you've gotten to a point where everything seems really difficult, you might ought to double back, do a little careful exploring in easier areas, and visit merchants to try to find some good high-quality components to make good gear from.