Download takes a long time to start, but download speed is then very fast

I have now also adapted my www.conf + restarted apache2 and php
but there was no improvement.

[www]
user = www-data
group = www-data
listen = /run/php/php7.3-fpm.sock
listen.owner = www-data
listen.group = www-data
pm = dynamic
pm.max_children = 5
pm.start_servers = 2
pm.min_spare_servers = 1
pm.max_spare_servers = 3
pm.max_requests = 500
env[HOSTNAME] = $HOSTNAME
env[PATH] = /usr/local/bin:/usr/bin:/bin
env[TMP] = /tmp
env[TMPDIR] = /tmp
env[TEMP] = /tmp

According to the article

updating to NC17 could resolve the problem
… ???

When downloading a file it’s over this link:
https://mydomain.de/remote.php/webdav/ubuntu-18.04.2-live-server-amd64.iso
May be there is a problem in remote.php or Webdav?

remote.php:

<?php
/**
 * @copyright Copyright (c) 2016, ownCloud, Inc.
 *
 * @author Brice Maron <brice@bmaron.net>
 * @author Christopher Schäpers <kondou@ts.unde.re>
 * @author Joas Schilling <coding@schilljs.com>
 * @author Jörn Friedrich Dreyer <jfd@butonic.de>
 * @author Lukas Reschke <lukas@statuscode.ch>
 * @author Robin Appelman <robin@icewind.nl>
 * @author Robin McCorkell <robin@mccorkell.me.uk>
 * @author Thomas Müller <thomas.mueller@tmit.eu>
 * @author Vincent Petry <pvince81@owncloud.com>
 *
 * @license AGPL-3.0
 *
 * This code is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License, version 3,
 * as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License, version 3,
 * along with this program.  If not, see <http://www.gnu.org/licenses/>
 *
 */

require_once __DIR__ . '/lib/versioncheck.php';

use OCA\DAV\Connector\Sabre\ExceptionLoggerPlugin;
use Sabre\DAV\Exception\ServiceUnavailable;
use Sabre\DAV\Server;

/**
 * Class RemoteException
 * Dummy exception class to be use locally to identify certain conditions
 * Will not be logged to avoid DoS
 */
class RemoteException extends Exception {
}

/**
 * @param Exception|Error $e
 */

image

Anyone a idea how to reduce this? TTFB