A mistake that is common in the conversion of C to F when you look at tolerance is the fact that the conversion is not the same conversion for measured temperature.
1°C is equal to 1.8°F. Both have a different starting point, which is why when using the measured conversion formula of T(°F) = T(°C) × 9/5 + 32 you are adding or subtracting 32 in the process.
When looking at tolerance you should stick to the ratio of C to F or 1:1.8
For example, ±15°C is equal to 15 x 1.8 = 27°F. if we were looking at measured temperature we would be looking at. 15°C × 9/5 +32 =59 F.