Problem: "admin-ajax.php?action=wordfence" slowing down website

Dear all,
I recently checked my website speed with pingdom and apparently a file/path which includes “wp-admin/admin-ajax.php?action=wordfence” is responsible for the slowing down of my website. I had previously installed Wordfence as a plugin and removed it afterwards. The html however still shows up. What can I do to remove it? Should I install Wordfence again? I really want my site to be faster.

Thank you very much for your support!

Best regards,

Christian