My shell was taking 2 seconds to start, after a bit of commenting out in .zshrc I narrowed it down to the rbenv init -.

Some Google time later I found that rbenv rehashes all gem during the init process and this can be stopped by changing it to rbenv init - --no-rehash.

I also took the time to remove oh-my-zsh plugins I didn’t use very often and change my theme to miloshadzic which does not display the Ruby version.

Now my shell starts “instantly”.