We report a high-energy, picosecond, mid-infrared (MIR) optical parametric oscillator (OPO), in which a length of hollow-core-fiber (HCF) is employed to enable operation at 1-MHz repetition rate in a compact cavity format. The OPO is synchronously pumped by an ytterbium-doped-fiber (YDF) master-oscillator-power-amplifier (MOPA) system, seeded by a 1040-nm gain-switched laser diode (GSLD). Using periodically poled lithium niobate (PPLN) as the nonlinear crystal, the OPO generates signal and idler beams with tunable wavelengths in the range of 1329-1641 nm and 2841-4790 nm, respectively. The OPO provides 137-ps pulses with a maximum signal energy of 10.05 µJ at 1600 nm and a maximum idler energy of 5.13 µJ at 2967 nm. This, to the best of our knowledge, represents the highest energy MIR pulses, as well as the highest total converted pulse energy (15.18 µJ), ever achieved from a fiber laser pumped picosecond OPO.