I have an older computer and lag can be a problem from multiple points from me. (PC/ISP/SE SRV) I found some things that helped me.
-In {System Settings} & {Character Settings} : I adjusted the amount of stuff i request to load like people and effect animations. At first this sounds like a loss, but, in all reality I didn't change the textures for the world or my own char. So i don't notice a difference.
-Frame Limiting : I set this aside as it may have nothing to do with anything. I set mine to limit because it would go from 35+ to 0 to 5 to 0 to 18 ..... etc and it almost seemed like it would pull to high top out crash and have a seizure, and limiting it and then restarting the client has stopped it from Seizen up. I still get a few slight jumps but overall smooth
-Misc Stuff : i use an Application Called Razor (Sorry for naming a product ) but its a game booster and when i launch FF XIV with it it will cut all un needed stuff running in my computer and free up Phys mem and CPU load . It has helped . Not saying get that program but looking at your Physical Memories load % & your CPU's Load% freeing up space and clutter always helps even the best pc.
Just sharing my experience, cause i know the feels of crippling lag..... They suck
