Hey there @Team_Disorder! Welcome back to the community! So it’s dependent on which method you’re using. If you’re using level composition and level streaming, you’d just load your sub level on top before you teleport the player there, and you’d just keep your persistent level in until you needed to leave it. This can be accomplished by loading and unloading the stream levels.
Alternatively if you’re using World Partition, you’re going to want to make level instances and use data layers the same way. You’d have your persistent world basically, and just preload wherever you would teleport to. This doesn’t take you to a new level so the massive load shouldn’t occur, but you will still need to account for time it takes to load, which depending on your assets could be quite fast or just as long!