Ultima IV was about as big-budget as a video game got. Here are the credits for the DOS version: https://www.mobygames.com/game/dos/ultima-iv-quest-of-the-av...
19 people, total, for the original development and production on the Apple II version, plus the PC, Atari and Amiga ports.
Still it was much smaller. Witcher 3 dev team is about 250.
Still it was much smaller. Witcher 3 dev team is about 250.