  SXP 15.3 and SXP 305 are two Be X-ray binaries in the Small Magellanic Cloud
that are spatially separated by ~7 arcsec. The small separation between these
sources has, in the past, resulted in confusion about the origin of the
emission from the combined region. We present long-term optical and X-ray
monitoring results of both sources, where we study the historic and recent
behaviour. In particular, from data collected as part of the S-CUBED project we
see repeating X-ray outbursts from the combined region of the two sources in
the recent lightcurve from the Neil Gehrels Swift Observatory, and we
investigate the origin of this emission. Using the H-alpha emission line from
the Southern African Large Telescope (SALT) and photometric flux from the
Optical Gravitational Lensing Experiment (OGLE) to study the changes in the
size and structure of the Be disc, we demonstrate that the X-ray emission
likely originates from SXP 15.3. Timing analysis reveals unusual behaviour,
where the optical outburst profile shows modulation at twice the frequency of
the X-ray outbursts. We consider either of these periodicities being the true
orbital period in SXP 15.3 and propose models based on the geometric
orientations of the Be disc and neutron star to explain the physical origin of
the outbursts.
