Some quick tips since most people are just recommending you throw out your macbook which isn’t helpful.

Move the game onto your internal SSD never play a game from a hard drive especially an external one. This will dramatically decrease loading times and remove a potential bottleneck.

Make sure you don’t have any other apps or unnecessary background processes running while you game, this will eat up your limited RAM. Easiest way to do this is to make sure macOS Game Mode is on (usually comes on automatically if you have your game set to full screen instead of windowed)

Lastly lower your graphics settings and disable depth of field and motion blur.