Try changing the rendering system on that first popup to either OpenGL or Direct39 (I'm not positive on the accuracy of those names but you'll see what I mean.)
Here's a few things you could try and maybe this will cut down your lag issue.
- Have you tried getting the light version of the download instead of the full? The light is less lightly textured and not so heavy and it might help you there.
- Also, you can try and seeing if switching rendering systems could help, along with changing the in-game settings. Anti-Analysis, Water Reflections and Distance Viewer: Off / 0. That could help with your lagging issue.
- Have you tried using a different browser to login into the login tab altogether?