Not strictly correct as S1.5 came with the higher spoiler standard airbag and the S2 motor with ignitor module module in the ecu and other minor differences such as reversed coilpack mounting pattern. I am 99% sure that the S1.5 was phased out late 1995/early 1996.
If you have a cloth interior, S15/N15/ S2 R33 steering wheel, S2 Dash, S2 "rough" dash fascia, painted rear boot fascia, and S2 front headlights and front bar then you can be pretty sure its a S2... failing that read the S1/S2 FAQ as I cant be bothered pointing out anything else ...
FAST is still the 100% sure option though