The formula to convert degrees Celsius (°C) to degrees Fahrenheit (°F) is:

°F = (°C × 9/5) + 32

Plugging in the value of °C as 15, we get:

°F = (15 × 9/5) + 32

°F = (27) + 32

°F = 59

Therefore, 15 degrees Celsius is equal to 59 degrees Fahrenheit.