  We report the characterization of a massive (m_p=3.9 +- 1.4 M_jup)
microlensing planet (OGLE-2015-BLG-0954Lb) orbiting an M dwarf host (M=0.33 +-
0.12 M_sun) at a distance toward the Galactic bulge of 0.6 (+0.4,-0.2) kpc,
which is extremely nearby by microlensing standards. The planet-host projected
separation is a_perp ~ 1.2 AU. The characterization was made possible by the
wide-field (4 sq. deg.) high cadence (Gamma = 6/hr) monitoring of the Korea
Microlensing Telescope Network (KMTNet), which had two of its three telescopes
in commissioning operations at the time of the planetary anomaly. The source
crossing time t_* = 16 min is among the shortest ever published. The
high-cadence, wide-field observations that are the hallmark of KMTNet are the
only way to routinely capture such short crossings. High-cadence resolution of
short caustic crossings will preferentially lead to mass and distance
measurements for the lens. This is because the short crossing time typically
implies a nearby lens, which enables the measurement of additional effects
(bright lens and/or microlens parallax). When combined with the measured
crossing time, these effects can yield planet/host masses and distance.
