I've heard a bunch of people complaining that their levelling experience has been ruined because its so insanely slow now. Also there were some people who did some testing on the PTR and said it was about 5-10% longer (roughly) to get to 110. But I've been levelling allied races for their heritage armour and I'm not seeing a problem. True I haven't levelled a character from scratch since MoP. So it's been awhile. But I get about 1 level for a dungeon (without quests). And about 4-6 quests give me a level. I did a dungeon gained a level and then literally 5-10 minutes of questing and I gained another level. This seems like a perfectly reasonable pace for me. To clarify I did all of this with heirlooms. It doesn't feel dreadfully slow or anything. I've yet to see confirmation but I heard that low level quests got their EXP boosted which would've made up for the increased time it takes to kill things.