Hi,
Are you really sure that you download 1.5GB through another extension and not download the file directly in the server ?
Because there is a huge difference between calling a PHP page which will send you "manually" a file (with the time limitations we know) and download a file directly in the web server (without time limitation because there is not PHP, it is a classical download).
Redirecting the user to another url works but it is not something safe because everybody can access to the file with the right url.
What I can propose you is a little patch in order to use "readfile" instead of reading manually the file.
I know that there is something strange with the output buffering so we can try to avoid it.
You have to make some replacement in the "administrator/component/com_hikashop/classes/file.php" file.
		header("Expires: 0");
		header("Last-Modified: " . gmdate("D, d M Y H:i:s") . " GMT");
		header('Content-Type: application/octet-stream');
		header('Content-Disposition: attachment; filename="' . $name . '"');
		header('Content-Length: '.($seek_end - $seek_start + 1));
		header("Cache-Control: maxage=1");
		header("Pragma: public");
		header("Content-Transfer-Encoding: binary");
		$fp = fopen($filename, 'rb');By:
		header("Expires: 0");
		header("Last-Modified: " . gmdate("D, d M Y H:i:s") . " GMT");
		header('Content-Type: application/octet-stream');
		header('Content-Disposition: attachment; filename="' . $name . '"');
		header("Cache-Control: maxage=1");
		header("Pragma: public");
		header("Content-Transfer-Encoding: binary");
		if($seek_start == 0) {
			header('Content-Length: ' . filesize($filename));
			if(!ini_get('safe_mode')){
				set_time_limit(0);
			}
			while(ob_get_level() > 1)
				ob_end_clean();
			flush();
			readfile($filename);
			exit;
		}
		header('Content-Length: '.($seek_end - $seek_start + 1));
		$fp = fopen($filename, 'rb');So it will use the "readfile" function if you are not trying to use the "resume download" feature.
By flushing and cleaning the output buffering, I hope that your server won't block anymore the sending of the file.
Regards,