Try assigning a static IP address to the HP that is outside of the DHCP range specified in your 615. Also, temporarily disable WPA security in the router, and see if you can now connect successfully with the HP printer.
If the answer is Yes, now set up the wireless. Your printer supports wireless N, so it will support the cipher you have set, but your best choice, if compatible with your other wireless devices, is WPA2 only + AES; this will give you the best security and the best performance.
You may also want to check to make sure you have enabled N wireless, under the Wireless settings. If you don't have any G wireless devices, select N only. Otherwise, unless you have some old B devices, select G,N combined.
You can also experiment with the Channels. If you currently have auto 20/40, select 20 and see what happens. Also, have you hidden the SSID by making it Invisible? Make it Visible and see if that fixes it.