i can assure you GM never referred to it as "1.5".

the cable you need is one that uses the OBD1 communication protocal, just with an OBD2 connector on the end. it won't work with any OBD2 vehicle, or at least not in the capacity you would need it for. GM kept the ALDL scheme around for quite some time after 1996, called the "UART data link", so you could poll data off of it, but not much useful stuff for tuning.