What is mesh optimization?

Hi,

I spent a few minutes making the model of a lamp with blender. It is a quite simple shape because it's just a cone with a negative part and a few connected cylinders.

However, once added to my game, it started to lag. When I removed the item, the lack of lag proved it was the source of the problem. Is there a way to reduce small details in these little objects? I've seen a lot of other games that run perfectly fine with much more complicated shapes.