We are really sorry that you are facing issue importing the the demo content.
Can you please clarify that you are having issue with the Agency Demo only or importing any other the demo?
This issue may be due to you PHP memory allocation. Please check below.
Contact your host to increase your allocated memory or do it yourself by adding this code in your wp-config.php define( 'WP_MEMORY_LIMIT', '256M' ); define( 'WP_MAX_MEMORY_LIMIT', '512M' );
Also please check this post do needful.
In case the issue persists, would you mind providing us with login credentials so we can take a closer look? Please provide following information: Set it as Secure Note