The lag that is usually noticed is with weaving abilities. So it can become a lot harder to double weave them between the GCD, or you can experience things such as pressing Swiftcast and then if you press the Resurrect button it starts casting when it's meant to be instant, because it hasn't received permission from the server yet to make it swift.

There has been significant issues with NTT in the last few months on NA worlds increasing ping by 200 and in the last few days this has especially affected people in Europe apparently. Many people have been getting around it with a VPN.

Although the lag may be worse for you right now if you play on an NA world, I do remember EU worlds being less reliable for lag and connection overall in the past, but my memory of this was many years ago and it could be better now.