Imo there isn't really that much lag or lagspikes lately, even in EU primetime. There's a slight delay yeah, but nothing that would really hamper you. It was much worse ~2 months ago or so. But yeah, PvE realm will further help with that, but more so about some zones being overcrowded, which is the bigger issue :p
Level 29 so far on my warlock, been taking it slow, leveling almost exclusively with rested xp so I don't have to grind in between