Magento2 Creating a new directory

you can use \Magento\Framework\Filesystem\Io\File.
Either inject an instance of it in your class or instantiate it manually using new.
Then do this:

/** @var \Magento\Framework\Filesystem\Io\File $io **/
$io->mkdir($this->directoryList->getPath('media').'/import/images', 0775);

Also, the problem might be because your rights say '775' as string. Try changing it to 0775.