Yes, the rss feed is cached. And it is cached for 1h.
Go to administrator/components/com_comment/plugin/com_content/com_content.class.php -> find the createFeed function and then find the line:
$rss->useCached("RSS2.0", $folderPath . DS . 'joscfeed' . $contentid . '.xml');
change it to
$rss->useCached("RSS2.0", $folderPath . DS . 'joscfeed' . $contentid . '.xml', 600);
this will change the cache time to 10mins instead of 60. I don't advise you to remove the cache, as the creating of the feed is resource intensive. If you have a lot of users subscribed to the feed this can slow down the page generation.
Kind regards,
Daniel