Just as Vanroe suggested, try out those, I have 25mb down/2.5mb up and never had lag during alpha, beta 1, and 2. But started seeing more and more lag, specially once I hit Titan HM it was to a point I couldn't play. (couldn't dodge land slide even if I did on my screen)

Pingzapper lets you try out for free forever with a 1 hour per usage restriction, so you may want to try it out using that, if it works, I know it sucks but buying monthly subs to keep the connection going would be good. I didn't want to pay extra but at same time I want to keep on playing XIV so I just paid it, you get 2 simultaneous connection so if you're like me with me and my wife both playing, it covered both of us.

Aside from this we can only hope it gets fixed from SE's/ISP's end.