VR preview should work right, maybe try to exit out of simulate before hitting play on VR preview. If that isn’t the issue, remember that you need to plug in the leap NOT into the oculus usb port, but rather its own, since it is a bandwidth hog and will not be happy with shared bandwidth. The other thing to remember is that you need a pretty powerful computer to hit 75fps on the oculus. If you hit both of those and you see your left hand, your elbow->wrist should be 1:1 and very smooth. The hands may differ slightly due to rigged mesh geometry.
Feel free to rescale bones if you want that fully 1:1 experience.