You can try disabling Players.CharacterAutoLoads, it will prevent players from auto spawning (and respawning), which also means you will need to manage respawns yourself but i assume that is what you want.
You can then call LoadCharacter() on any player you want to spawn/respawn.
(i forgot to mention that if you want to remove the character afterwards you can just use :Destroy() on their character, you can use LoadCharacter() to add it back later!)
(alternatively you can parent the player character to something else like ServerStorage if you want to TEMPORARILY remove it, you can then just parent it into workspace when you want them back again)
Can you show me the code that handles the spawning? (If there is one, can i have a link to the game to test it myself? It is possible it is just related to performance problems with your machine)