With the recent 1.8.1 update my wife and I have started to notice a tremendous slow-down compared to how Minecraft used to run. My wife will load a world on the Switch and while it is still loading I can connect to it on the computer well before she ever spawns in. It takes a good minute for the game to finish saving after we're done playing as well, which may not seem like a long time but since we're trying to turn the system off most of the time it's pretty noticeable. The interfaces for chests/crafting benches, etc. sometimes lag opening even when only 1 person is active in the world and it is far, far worse when we're connected online even for the host (which for us is the Switch because we play together on my wife's world).

I thought it might be related to the number of entities in our base but it doesn't seem to improve even when we're both far enough away from our base to keep it from loading. Basically, overall performance on the Switch just seems to be drastically reduced recently.

Edit: Added a video to show the type of generally poor performance we've encountered. In the second half the player on the bottom (myself) hits an invisible wall on already loaded chunks apart from the other obvious signs of lag.