The different training rates are linked to the anaerobic threshold. You can therefore also determine fairly well based on your 10 km time, what your achievable times are at the other distances. In this case, it applies that for the longer distances have done sufficient endurance training.
In 15 / 16.1 km and 20 / running speed 21.1 km take the sometimes rather off. This is correct: 15 / 20 km time is rounded down, the 16.1 / 21. 1 km time up.