FitzTheRuke
Legend
Do you mean you stopped assigning experience points during Phandelver once the players hit 3rd level? (Doubt that would go over well with my players.) But Hoard is still a challenge when starting with level 3 PCs?
I'm running Hoard for two different groups (starting at first level, but allowing leveling during Chapter 1) and I can't imagine it being too easy for level 3 PCs from the get-go. They'll just be able to accomplish more without resting. Replace a few cultists with Dragonclaws here and there, and it's good to go. I'm not sure you even need to do that, but it makes it more exciting.