Why are my emails taking a long time to send?

Check the content of the email. Is the content too long or is the email full of images/attachments?
Check your internet connection. Is your connection stable?
Check the server. Is the server where you are trying to send your email from having technical issues?
Check other emails you send. Are all emails taking a long time to send, or just one specific one? If it is just one, further investigate the content of that email.
Check that you are authorized to send emails from the server. Did you set up the correct credentials and authentication?