I got VoH couple days ago, and manages to play through the main story of the addon.
When i started doing exploration and dungeons, i started getting severe lags, sometimes 5-10 seconds of rubberbanding and whatnot.
Prior to getting the addon, i had no lags, not even with downloads or streams running in the background.
When i go to other regions, the lags disappear, usually they only appear in Nahantu and dungeons within the region, although i had lags in pit-runs as well.
I tried other games (WoW, D2R online, D3, other games), with 0 lags and stable sub-50 ping.
But in D4 VoH, ping is constantly >500 in Nahantu, <100 in other regions (which is still rather high for my connection).
Edit:
Ok, after a bit more playing, turns out the lags are everywhere. Only started after i got the addon, had no issues before then when i leveled 3 characters…and all other games work just fine.