You wont have to change ISP, becuase the game is new and most ISP's use a sandvine system for automated throttling. the ISP's just need to update the detection ruless.
When you look at the fact there are few who have the ISPs in this thread. while others in the same area as you who are on a different ISP who don't have the problem. It's clear on who is at fault.
Edit:
And for those who still don't believe this:
http://forum.square-enix.com/ffxiv/t...P2P-throttling
http://forum.square-enix.com/ffxiv/t...=1#post1107574