Singapore to Paris is about 10,724 km and usually takes around 15h in the air. The track it follows runs over the Eastern European plains, Central Europe, and Western Europe.
Over the Eastern European plains, Central Europe, and Western Europe the air is usually calm and settled. This track threads jet-stream latitudes, so in winter you may feel a few minutes of light, choppy air high up; summer usually rides calmer.
A flight this long spends hours at a high, smooth cruise. Even when one stretch is bumpy it is a small slice of the whole trip, and the aircraft treats it as routine.