While I can't confirm with 100% certainty. Based on optimization suggestions from the wiki, and anecdotal evidence It seems like having too many characters in your roll20 game can cause performance issues, especially if your game is using a character sheet that is a bit beefy. One idea I had to resolve this was to make minor NPCs into handouts instead of full blown characters, but you lose the functionally of tokens linked to the character, and any attributes or macros you might wish to implement yourself. What I would suggest: If it could improve performance in games with 100+ NPCs, allowing DMs to enable or disable character sheets on a per-character basis. It could be a simple toggle in the attributes section of a character window, or perhaps a right click action in the journal.