Speaking of old and universe specific, FASA used to publish an infantry skirmish game set in the Battletech universe called Battletroops. It was the first miniatures game I ever played (though I only ever used cardboard counters), and it was decent but quirky using map sheets with dots laid out in a hex pattern for movement. Figures moved individually and had a number of movement points to spend which were modified by armor, experience and wounds. MP would also be spent to place firing arcs (the more MP spent, the wider the arc) and most firing was done in the opponent's movement phase. The exception was area effect weapons, which were fired in the player's own movement phase using MPs.
It also integrated with Battletech to add 'mechs and vehicles to the game. In fact, my very first games of Battletech were played out in Battletroops using the Battletech Compendium. There was also an expansion called Clantroops that added power armor rules. Of course it's long out of print, but used copies aren't terribly hard to come by.
Additionally, FASA had a game called DMZ: Downtown Militarized Zone. I never owned that one, but my understanding is that it is the same basic game system, but set in the Shadowrun universe.
ETA: I should add that these games were officially 25mm. Scaling them to 15mm is not difficult, however. This is especially true for Battletroops since fullsize images of all the counters, templates and maps are on Board Game Geek. Going mapless should also be relatively straightforward, though square bases might be helpful in that case to assist in lining up firing arc counters.