1. The problem asks: How long does it take to charge a battery to 15%? 2. To solve this, we need the total charging time for 100% and then calculate 15% of that time. 3. The formula is: $$\text{Time for } x\% = \frac{x}{100} \times \text{Total charging time}$$ 4. Without the total charging time given, we cannot calculate the exact time for 15%. 5. If you provide the total charging time, we can substitute it into the formula and find the answer.