Extragalactic nova population studies have several advantages over Galactic novae. For example, a better overview of the nova population of an entire galaxy is obtained, and it of course makes it possible to study how the nova population depends on the Hubble type of a galaxy. Additionally, as all the novae in a given galaxy can essentially be considered to be at the same distance, it makes it much easier to identify the particularly luminous and sub-luminous novae amongst the population. The optical light curves of classical novae typically peak at around M(V) = -7.5, however the extreme lower or higher-luminosity eruptions can have M(V) > -6 or M(V) LT -10 respectively. Several luminous classical novae (defined as M(V) LT -9) were observed in the nearby M31 Galaxy during 2015. Here we present detailed spectroscopic and photometric observations, led by the Liverpool Telescope, Swift and the 0.65-m at Ondrejov, of these recent events, including M31N 2015-09c - one of the most luminous novae ever observed. We finally discuss these high-luminosity eruptions as a population, and compare them to the general nova population.