A scale can only tell you how much you are being affected by the Earth’s gravity. Some of the newer ones also say body fat and water percentages but they are not very accurate. Point is, scale weights aren’t giving you a full picture. How much food is in your gut, water retention, etc, it all fluctuates on a daily basis. It also sounds like your scale might be more on the inaccurate side…
I would only weigh yourself once a day after waking in the morning and vacating your bladder. And even then, expect it to fluctuate. The idea is to see a downward trend over time, not every day.
Finally, 15kg is not going to disappear overnight even on a dry fast. You can only realistically expect to lose 1-1.5kg of fat during a 72 hour fast, and that’s about the limit of what most sensible people will recommend. It’s possible to do more, but in my opinion the potential for problems starts outweighing the benefits at that point.
Day 1-3 you won’t lose anything. Day 1- you burn all the food contents in your stomach. Day 2 - you use up all your reserve energy. Day 3 - body depletes reserve energy and the shift to living on exclusive fat begins somewhere in this day. Day 4 - first full day of living on exclusive fat. Day 5 - continues. Day 6 - continues. Day 7 - continues…plateaus. Fat burn reach its maximum and the body cycles down its energy usage (fat demands) going Day 8 and beyond. Body is burning fat at a stable rate. It’s best to reach Day 4 of dryfasting to see actual fat consumption of brown fat.