Terrible Lag on One PC, Not the Other

I bought a new ASUS ROG laptop about 6 months ago and it has always had terrible lag while playing FFXIV. There's a second or two of delay before every action, which causes some abilities to go off twice or not at all. It's borderline unplayable, and certainly not fun.

It definitely seems to be connection related, but my homebuilt desktop PC is running the game perfectly on the same wireless connection, and the two computers are sitting right next to each other. Switching to a wired connection makes no difference. When downloading Heavensward, or any patch for that matter, my desktop download speed is about 4 Mb/s, while my laptop's is 0.5 Mb/s.

This is the only game that my laptop has this issue with. I play pretty much all the Blizzard games and they run the same on both computers. The only major difference between my two PCs is that my laptop is running Windows 8 and my desktop is on Windows 7.

I haven't been able to find any information that has helped me resolve this issue, and I'm getting pretty frustrated, so if anyone has any ideas I'm up for it.