[Help] Convex mesh collider lag

I'm following a tutorial to make a Bowling game.


Originally the bowling pins consisted of a parent game object with a rigidbody, a child object that has the mesh renderer, and another child object that had a Convex mesh collider [see Screenshot 1]. There are 10 bowling pins in total


The game was running smoothly (at around 90 FPS). However, later into the tutorial, the instructor modified the pins so that it's a single object (i.e. the bowling pin is now a gameobject with the mesh renderer, a convex mesh collider, and a rididbody) . Now the game runs at around 2 FPS. [see Screenshot 2]


What's going on here? The game was running fine before making the modification. Putting all the components into a single game object shouldn't have an effect on the performance.