Yes, your heels hit first when you walk. If you are trying to walk fast, you will overstride or lengthen your stride, which will cause you to hit your heels harder. So you may need to slow down a little or consciously shorten your stride. The only way I can walk fast and keep up with other fast walkers while wearing minimalist footwear is to run. Which is why I go hiking in running shoes that have enough cushioning that I can walk fast without having to run.
Female, 5'3", 50, Max squat: 202.5lbs. Max deadlift: 225 x 3.