I've experienced severe performance issues, particularly with loading times in Singleplayer.

The world I've experienced this the most on is 80.4MB in size, on Render Distance 10, Simulation Distance 6, with Fancy graphics turned off.

When near the ocean there is a noticeable degree of mild lag, which is amplified whenever the game saves, which occurs very frequently.

When travelling on the ocean by boat the lag is dramatically amplified and the chunks load so slowly that you can legitimately catch up to the invisible wall where the next chunk is meant to load and spend upwards of 2 minutes just waiting for it to render. When it does load, you can only see about 3 chunks directly ahead of you and after roughly 1 minute the process repeats.

At random intervals on the ocean, especially when waiting for chunks to load the game will randomly freeze but still keep going in the background. despite there being no audio or visual indication of this, when this happens on any difficulty other than peaceful when the lag subsides OR if you EXIT THE APPLICATION the moment you return to the world you will find that you had somehow died. This particular problem has occurred approximately 5 times in the past week alone.

And, especially during saving, and immediately after loading into the world for the first time menus, chests, and the inventory will lock you in place and after 5 seconds a loading bar will appear, an after about 5 more seconds you will be able to access/leave the menu/inventory/chest.

These problems are also exacerbated further the more of the world you have explored. After exploring quite a lot of places and returning to my main base, an area which was lag-free before I went to explore the world, I returned to find that the game lagged constantly (although I can't be sure, it's safe to say it remains at close to 20 FPS)