I played EP circa 2002 or so myself, but I was aware of IS even then because I looked it up online. SMT games were still pretty much a cult favourite during those times, but there were sites dedicated to the duology that provided a lot of information about the games. Persona 2: Eternal Punishment was actually my gateway to this multiverse (then it was SMT, Kuzunoha, Persona 1, DDS) but the artstyle, the concept, the plot and characters were extremely interesting so I looked it up to see if there was more to the world, since I was raised on JRPGs that had 10 million titles under its series, haha. I played IS a few months after the patch was released because I had great timing and just finished a replay of EP and wanted to reread something about the universe of Persona. Happened to see news about the patch and. Ta-da~ It's not as popular as P3 and P4 but it did generate 700k or so of sold units for the remake (for P2:IS, don't actually know how much P2:EP get). I think it's one of those unpopular popular titles that a lot of people know even if not a lot has played it.