How to Enable Port Forwarding for Litecoin Mining?
There are countless router port forwarding guides on the Internet, this isn't Bitcoin/Litecoin specific.

Anyway, you've got the port right, you need to set your computer up on a reserved local address so that your internal IP address doesn't change when you reboot. Then you need to assign that custom "game or application" you have created to your newly reserved local IP. You may need to allow the port on your computer's firewall too. That should do it.

Saying that, Bitcoin/Litecoin is peer-to-peer and doesn't require the port opening it will function fine without it. The only difference will be that people are able to connect to you which will give your node more peer options so it could make it sync faster. Of course it could also make you sync slower because you'll be helping more peers sync.

Depending on your Internet speed it could be the uploads that are making your downloads take aeons, or it could be a slow/busy disk. Remember, it's not a website - you're not going to download 4Gb from the other volunteer peers at the same rate you might for other downloads.