Is Legacy Adv Fog of War supposed to be so laggy?

I'm just coming back to roll20 and ran a game with dynamic lighting for the first time. I've decided not to use "Updated Dynamic Lighting" because of the lack of enforced line of sight but when I turn on Advanced Fog of War in legacy, the game slows to a crawl. I tried this feature on my main PC and my Laptop and Surface Pro, my internet is pretty fast but in every case it lags terribly for my friends and I. Just wanted to know if Adv Fog of War has always been this laggy or am I doing something wrong settings or anything else wise?

The most common cause of lag on Legacy DL is the combination of Advanced Fog of War and Global Illumination. If you have both of those on simultaneously, that will usually kill performance. Try turning off one or the other if this is the case.

I have global illumination off. Funny thing is that when I turn off legacy and switch to updated "explorer mode" there's zero lag. But I really want line of sight so I don't want to use updated until it has that feature

Interesting. I have never run into substantial lag from either system, but then, I don't use (Advanced) fog of war. If you want to retain some of that functionality but continue to use Dynamic Lighting, you could try what I use:  Light Crumbs .