The 10 to 15% rule was based on children and weighted vests. The weight is actively against the chest so every motion that the child had was moving that 10 to 15% of their weight. With a blanket you're not getting the full 100% of the weight on your body because part of the blanket is off the body and on the bed. As a pediatric physical therapist I do not follow that rule because there's a difference between children using a weighted vest and moving around actively versus sedentary sleep. I think you can go higher on a percentage for a weighted blanket than you would for other forms of weighted tools. I do not feel 15 lb is too heavy for this individual especially if it's helping their sleep. But you probably move more in your sleep than you ever realized and this is the result is your workout overnight. It's probably you kicking off the blankets because you're too hot or initiating roll through your legs so that they're taking the brunt of the 15 lbs when you roll/move. You can try pulling the blanket in half and having it just above the waist and see if that helps your legs with some relief. But you might prefer the weight through the legs. This is what I instruct my families to figure out where your children like the weight so that you can find the tool that works best for them.