If you see that demo content import process loading forever, got not all content imported or incorrectly working demo content this means your hosting PHP.ini limits too low for working with WordPress Importer and demo data can't be imported on your hosting without correct configuration.
You should contact your web hosting support and ask them to increase those limits in PHP.ini to this values:
- max_execution_time = 300 (600 recommended)
- memory_limit = 128M (256M recommended)
- post_max_size = 32M
- upload_max_filesize = 32M
- max_input_vars = 2000