About 20,000 entries in the Zsh history slowing it a little. All completion activated (but zcompile'd, along with a very large digraphs.zwc).
I think most would not be troubled by taking 1.06X longer, though, especially at this 8 ms scale and for interactive session initiation. Note this test upper bounds Time To First Prompt { a different "TTFP" from Time To First Plot ;-) }, since it also exits as part of the `-c`.
Chances are, like in the article, you installed oh-my-zsh, a third party configuration framework.