  We show that the Planck 2015 and BICEP2/KECK measurements of the Cosmic
Microwave Background (CMB) anisotropies provide together an information gain of
0.82 +- 0.13 bits on the reheating history over all slow-roll single-field
models of inflation. This corresponds to a 40% improvement compared to the
Planck 2013 constraints on the reheating. Our method relies on an exhaustive
CMB data analysis performed over nearly 200 models of inflation to derive the
Kullback-Leibler entropy between the prior and the fully marginalized posterior
of the reheating parameter. This number is a weighted average by the Bayesian
evidence of each model to explain the data thereby ensuring its fairness and
robustness.
