Theoretically, there were 25-30 characters on the hero side of Infinity War: Iron Man, Thor, Captain America, Black Widow, Hulk, Vision, Scarlet Witch, War Machine, Falcon, Star-Lord, Rocket Raccoon, Groot, Gamora, Drax, Mantis, Nebula, Doctor Strange, Wong, Spider-Man, Winter Soldier, Heimdall, Black Panther, Okoye, Shuri, M’Baku, Eitiri, Nick Fury, and Maria Hill. That doesn't even include villains or side characters.
I saw an interview (can't remember which one), where one of the cast members mentions that if every character (villains included) got 5 minutes of screen time, the movie would have been over 4 hours long or something like that.
Actually, I don't know if anyone has timed it, but I'm willing to bet that War Machine MK1 was only in Iron Man 2 for 10 minutes or less (screentime).