15k steps taken in an easy stroll is worthless compared to 100 hard earned steps up a steep hill, mountain, stairs etc. People like to use 10k or 15 k steps but its always quality over quantity for me. Besides if you want to do real cardio get on a bike. Walking 15k is tiring but you can burn the same calories (if not more) in less than half the time with more intense exercise. Intermittent Fasting requires no physical energy but you can lose more weight than walking 15k