There are usually three assumptions "built in" to those 10 and 15 pound weights:

1. There's an assumption that it's a summer (3-season) load, so there is minimal clothing and a lighter sleeping bag. Depending on what part of the country you live in, warm clothing and a warm bag can add significant weight - there's about a 5-pound difference between my July and January loads.

2. There's an assumption that you'll filter water as you go, and (at least in my typical load) that you'll start out with only one liter of water. Carrying extra water drives pack weight up fast.

3. For most of the 10-15 pound claims, it's a "base weight," not a fully loaded weight. The weight includes only things that you'll take in and bring out with you; it does not include consumable items like food, water, and stove fuel.

In the summer, I usually leave the trailhead carrying my gear, two days worth of food (a pound a day, for me), a liter of water, and a small fuel canister (110-gram size.) My "base" weight is about 14 pounds in the summer; my "put it on my back
and start walking" weight is usually 19 or 20 pounds.