Feedback form hangs due to PHPMailer - phpmailer

Question

I have a feedback form, this script is filtering and validating data and writing data to the database. At the very bottom, through include, I connected a script with PHPMailer, which sends the text of the feedback form to my mail via gmail smtp.
If I comment out the script connections, then the form is submitted either immediately or after 1 second. With him, he can wait 2-3 seconds.
I submit form data via XMLHttpRequest, remotely. Upon successful submission, the form is reset to zero and the submit button becomes inactive, and via pop-up notifications I display the server's response. So it happened that I managed to press the send button 2-3 times until the script worked and, accordingly, several records were created and several letters were sent to the mail. Is this how it should be or have I configured PHPMailer wrong?
Let me know what data I need to attach. This is my PHPMailer script:
<?php
use PHPMailer\PHPMailer\PHPMailer;
use PHPMailer\PHPMailer\Exception;
require $_SERVER['DOCUMENT_ROOT'] . '/form/PHPMailer/PHPMailer.php';
require $_SERVER['DOCUMENT_ROOT'] . '/form/PHPMailer/Exception.php';
require $_SERVER['DOCUMENT_ROOT'] . '/form/PHPMailer/SMTP.php';
$mail = new PHPMailer;
$mail->CharSet = 'UTF-8';
$mail->isSMTP();
$mail->SMTPDebug = 0; // 0 = off (for production use) - 1 = client messages - 2 = client and server messages
$mail->Host = gethostbyname("smtp.gmail.com");; // use $mail->Host = gethostbyname('smtp.gmail.com'); // if your network does not support SMTP over IPv6
$mail->Port = 587; // TLS only
$mail->SMTPSecure = 'tls'; // ssl is deprecated
$mail->SMTPAuth = true;
$mail->Username = 'mymail#gmail.com'; // email
$mail->Password = 'mypassword'; // password
$mail->setFrom($email, $name); // From email and name
$mail->addAddress('mymail#gmail.com', 'Admin'); // to email and name
$mail->Subject = $subject;
$mail->msgHTML("Message from: \n"."<h3>".$email."</h3>\n"."<h1>".$message."</h1>"); //$mail->msgHTML(file_get_contents('contents.html'), __DIR__); //Read an HTML message body from an external file, convert referenced images to embedded,
$mail->AltBody = 'HTML messaging not supported'; // If html emails is not supported by the receiver, show this body
// $mail->addAttachment('images/phpmailer_mini.png'); //Attach an image file
$mail->SMTPOptions = array(
'ssl' => array(
'verify_peer' => false,
'verify_peer_name' => false,
'allow_self_signed' => true
)
);
$mail->send();
// if(!$mail->send()){
// echo "Mailer Error: " . $mail->ErrorInfo;
// }else{
// echo "Message sent!";
// }
?>

Answer 1

You're doing some inadvisable things here.
$mail->Host = gethostbyname("smtp.gmail.com");
This sets Host to a literal IP address, and that in turn means that you will never have it match a TLS certificate name. As a result you're having to disable TLS verification, which is never a good thing. If you understand exactly why you're doing this, and what the consequences are, that's fine, but if not, you shouldn't be doing it.
There isn't any error checking in this script. I suggest starting again using the gmail example provided with PHPMailer which is much more careful.
You've discovered why sending to remote mail servers with SMTP during web form processing generally a bad idea: it's too slow, partly by design. The best way to work around this is to install a local mail server (postfix is good) and configure it as a relay to your gmail account – if you search for that you'll find plenty of examples. When that's done, you can submit messages to localhost, it will be more or less instant, and it will take care of queuing, throttling, bounces etc.