Is Using Smtp For Sending Emails Through Office365 Slow?

Dear Cs-Cart community,

I am using SMTP as a method of Sending Emails on my CS-Cart store. I am relaying to Office 365 account using the below configuration:

Method: via SMTP server

SMTP host:

SMTP username:

SMTP password:

Use Encrypted Connection: TLS

Use SMTP authentication: Checked

It works fine. However, it takes more than 20 seconds for the sending process to complete. So when placing an order, the buyer will wait until the order confirmation email is sent then the order landing page shows.
I contacted Microsoft and they advised that it shouldn't be such slow. They advised also to check with CS-Cart if this delay is common on CS-Cart platform.
So please, do you experience the same delay when using SMTP via Office 365?
By the way, I am using the latest version of CS-Cart (V 4.8.1).