I had this same issue too on my old laptop. The game ran just fine before that on medium-high settings, but afterwards even at the LOWEST settings the game was unplayable.
Once I did that, it got Lunia back up to normal and I could play it without lag on medium settings.
Depending on what gfx card you have, some will allow you to prioritize performance over picture quality. Honestly, I don't notice much difference in terms of picture quality between setting my gfx card to performance over quality/battery life. Worth a try.
You should also DEFRAG if you haven't already. Also downloading CCleaner helps a ton. All of these things combined won't fix the issue entirely, but it should make it a bit better.