image optimize Issue
When uploading images into Drupal, those are uploaded as it is and not compressed. To compress them you can check Image Optimize (or ImageAPI Optimize) Module.

Another solution is to add custom code in your custom module, which will compress image before a record is inserted into file_managed table, check code below:

/**
 * Implements hook_file_presave().
 */
function [MODULE_NAME]_file_presave($file) {
  if (!empty($file-&gt;filemime) &amp;&amp; (strpos('image', $file-&gt;filemime) &gt;= 0)) {
    $compressed = _[MODULE_NAME]_compress_image($file-&gt;uri, $file-&gt;uri, 75);
  }
}

/**
 * Helper function to compress images while uploading.
 *
 * @param string $source_url
 *   Source image URL.
 *
 * @param string $destination_url
 *   Destination image URL.
 *
 * @param string $quality
 *   Percentage of Image quality to compress.
 */
function _[MODULE_NAME]_compress_image($source_url, $destination_url, $quality) {
  $source_url = drupal_realpath($source_url);
  $destination_url = drupal_realpath($destination_url);

  $info = getimagesize($source_url);

  if ($info['mime'] == 'image/jpeg') {
    $image = imagecreatefromjpeg($source_url);
  }
  elseif ($info['mime'] == 'image/gif') {
    $image = imagecreatefromgif($source_url);
  }
  elseif ($info['mime'] == 'image/png') {
    $image = imagecreatefrompng($source_url);
  }
  else {
    return FALSE;
  }

  //save file
  imagejpeg($image, $destination_url, $quality);

  //return destination file
  return $destination_url;
}


NOTE: Change [MODULE_NAME] with your module name.