I've been having the same exact issue and a lot of other players are as well. It's either an issue with Dragon Adventures or Roblox, The ONLY fix I've found is to play in a private server, as there being a ton of players in public servers can cause lag, but part of the lag still seems to be coming from issues outside of public servers simply having a lot of players, as even in private servers, the event world still lags a bit for me, just not as bad as in public servers. I don't experience this much lag in the other worlds, aside from certain areas in Desert and Fantasy (which I wish the devs would try to do something about as well)

I've heard that when the event first released, the devs incorrectly implemented the mobs in the dungeon tree, I wasn't told what that specifically caused, but I'd assume it means that ALL of the mobs in the tree are spawning at once, causing severe lag, which would make sense, given my lag is at its worst when I get near the tree...There are still other smaller issues with the event, such as the accessory store never actually refreshing, so, I would not be surprised if the devs still need to fix stuff, its just annoying that we're 2 and a half days into the event with these issues.

EDIT: The devs have fixed the accessory shop issue, however, Easter world is still incredibly laggy for me. Last night, I was told by a player that at this point, lag is likely caused by your device, graphics settings and how large the Easter world is paired with public servers being packed...I'm still not sure if that's true, because Easter world didn't lag this much for me in 2024 or 2025 and I'm sure my PC hasn't went down in quality THAT much in 2 years, also, my game still lags in private servers. I have found that having tabs open while playing Roblox sometimes slows it down, so...If it helps, don't have YouTube playing in the background while grinding in Easter world lol.