php Mysqli中的登录验证速度很慢

Question

I have a login form with email and the password. For password I am using crypt() function to hash. My mysqli query is

 $stmt = $mysqli -> prepare("SELECT salt, password FROM table WHERE email=? ")) 
                {


                    $stmt -> bind_param("s", $email);


                    $stmt -> execute();


                    $stmt -> bind_result($salt,$password);


                    $stmt -> fetch();


                    $stmt -> close();
   }
   $password_encrypt = crypt($_POST['password'], '$2y$07$' . $salt);
    if ($password_encrypt != $password)
                {echo "invalid";}

question: For validation it takes 8 to 10 seconds. Am I doing anything wrong?

note: my form data is posting via ajax call.In my table email is indexed.