I found it in feed_widget.php at line 101

    public static function getSettingList()    {        $settingList['count'] = array(            'presentation' => self::PRESENTATION_SELECT,            'label' => OW::getLanguage()->text('newsfeed', 'widget_settings_count'),            'optionList' => array(5 => '5', '10' => 10, '20' => 20),            'value' => 15        );

Funny thing is optionlist looks like an array that should be shown in that backend somewhere but i cant find it. anyways i changed 'value' => 10 to 'value' => 15 and this did the trick. if there is an area in the admin panel i am missing please let me know.

Sorry all the updates. I found where it is. Insted of the admin panel its the settings on the front end of the site. Would be nice if this took a custom value though.

Thank you Paul for the  information. I was looking for this from last 1 week