Perhaps your game has a lot of parts and many scripts? What’s your graphics level on roblox player? Maybe you had a faulty plugin before and it’s already created a backdoor in your game. Check your scripts
Sometimes a game in Roblox will lag more than in studio due to complicated or unreliable scripts. I found a post where instead of just lagging the game more than studio, it completely froze it. See if this helps:ROBLOX Default Loading Screen Freezing