lag in creative mode

Hello,

 

When I am in creative mode, I have a lag from my screen. I would like to know why et how to fix it.

Material configuration type :

Imac 27 "- 2,8 GHz Intel Core i7 - ATI Radeon HD 4850 512 Mo - 8 Go 1067 MHz DDR3

Mac os version : 10.11.6 El capitan

Minecraft version : 1. 15.1 - java edition

 

Thank you

JP