We present results of the photometric (from 3 to 509 days post explosion) and spectroscopic (up to 230 days post explosion) monitoring campaign of a type IIb supernova (SN) 2015as. SN 2015as was confirmed as a stripped envelope SN of type IIb sub-class. The unique B-V colour evolution  suggests that SN 2015as does not show the early, short duration photometric peak. Post 75 days spectrum shows the transitioning from type II to type Ib nature of SN 2015as implying a partially stripped progenitor. The quasi-bolometric analytical light curve modelling suggests that the progenitor of SN 2015as has a modest mass (0.1 M_sun), a nearly-compact (0.05 x 10^13 cm) H envelope on the top of a dense, compact (2 x 10^11 cm) and a more massive (1.2 M_sun) He core. The [O I] and [Ca II] doublets in the nebular phase shows high asymmetricity in the explosion scenario. The intensity ratio of the [Ca II]/[O I] nebular lines favours either a main sequence progenitor mass of 15 M_sun or a Wolf Rayet star of 20 M_sun.