Environment:
Minecraft: 1.15.2
Carpet version: 1.15.2-1.3.15+v200318
Mode: Singleplayer and "open to LAN"

Issue:
When you spawn a fake player and set it's gamemode to spectator (for example to load an area) the mobcap still increases by 70 like it's in survival / creative mode.

that's normal - works like that in regular game. Use /gamerule spectatorsGenerateChunks false to disable that. just make sure not to stay in spectator with that disabled when closing the world - weird vanilla quirk