Email causes place order delay to thank you page.

I’ve noticed that having Woocommerce send a new order e-mail causes a significant delay after the “place order” button is pressed. I’m currently using an SMTP mailing plugin. When e-mails are being sent it takes an average of 8.4 seconds after pressing the “place order” button to get to the “thank you for your order” page. Without e-mails it’s 3.7 seconds. I’ve tested with multiple times with the same result again and again.

What should I do to fix this? Should I get an SMTP queue plugin? Why does WC wait until the e-mail is sent until it sends the customer to the “thank you” page?