Seems like Mega Man 5 in the Mega Man Legacy Collection has some issues. The game suffers from a lot of slowdown, more than what you'd experience if you were playing on an actual NES. There's only one fix right now and it's not really a fix! You can visit the options menu and change the games from Mega Man to Rockman. For whatever reason, the Japanese version of Mega Man 5 seems to run a lot better. Let's hope Capcom offers up a patch for this issue soon.