You can play it fine in a tablet, but i bet must be horrible on a phone.
Oh no, the game is always like that. It's because the engine wasn't designed to run a game from this size. A port to Godot is being made, but it will take years to get done.
The main issue is that the game keeps track of everything at the same time, so the more containers that you open, the more regions that you unlock... Will slow the game down. Some people used to skip the mansion for this reason.
Basically every single thing that exists in a run causes a small amount of lag/loading time. It is tiny but it adds up.