Comment 1 for bug 1475980

Sourceforge site is down for some reason and unfortunately hp-plugin utility is not able to fetch the plugin.conf from sorceforge site.
Can you directly download the plugin files from here:
https://www.openprinting.org/download/printdriver/auxfiles/HP/plugins/hplip-3.15.7-plugin.run
https://www.openprinting.org/download/printdriver/auxfiles/HP/plugins/hplip-3.15.7-plugin.run.asc

To install the plugin file you can run command 'sh hplip-3.15.7-plugin.run' in terminal or you can run command 'hp-plugin' in terminal and choose the second option to manually select the hplip-3.15.7-plugin.run file and install.

Run command 'hp-setup' to configure the print queue.