We report the discovery of HATS-15 b and HATS-16 b, two massive transiting extrasolar planets orbiting evolved ($sim 10$ Gyr) main-sequence stars. The planet HATS-15 b, which is hosted by a G9V star ($V=14.8$ mag), is a hot Jupiter with mass of $2.17pm0.15, M_{mathrm{J}}$ and radius of $1.105pm0.0.040, R_{mathrm{J}}$, and completes its orbit in nearly 1.7 days. HATS-16 b is a very massive hot Jupiter with mass of $3.27pm0.19, M_{mathrm{J}}$ and radius of $1.30pm0.15, R_{mathrm{J}}$; it orbits around its G3 V parent star ($V=13.8$ mag) in $sim2.7$ days. HATS-16 is slightly active and shows a periodic photometric modulation, implying a rotational period of 12 days which is unexpectedly short given its isochronal age. This fast rotation might be the result of the tidal interaction between the star and its planet.
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