  We present medium-resolution spectroscopy and multicolor photometry for the
optical transient PSN J09093496+3307204 (SN 2015bh) in the galaxy NGC 2770,
which has transferred into the supernova phase. The observations were carried
out between February 2015 to May 2016. Both at the phase of the SN impostor
(2015a) and at the supernova phase (2015b), besides Balmer emissions, the
strong Fe II emissions are seen in the spectrum; so, these spectra resemble
those of Williams Fe II type classical novae. The star is located near the edge
of a dark nebula and notably absorbed (Av = 1.14 +/-0.15 mag). Taking into
account this absorption, we determined maximum absolute magnitudes of Mv =
-15.0 +/-0.3 mag at the 2015a phase and of Mv = -18.14 +/-0.30 mag at the 2015b
phase. The light curve at the 2015b phase is similar to those of SN IIL. The
supernova progenitor is a luminous blue variable (LBV) star with the powerful
H{\alpha} emission. We considered several hypotheses of supernovae explosions
following optical transients related with LBV. The hypothesis of core collapse
of an evolved massive star interrupting the process of its merging with massive
companion in a binary system (a failed luminous red nova) was chosen as the
preferable one for this event.
