Imported scenes will be slightly larger as the thumbnail image is part of the scene data itself. That explains the larger size there. From your screenshot, your world is basically around 6-7MB, as the
packs folder is for compendiums and doesn’t really count as only the content in the
data folder will be sent to the user’s on load.
As for growing file sizes, see the FAQ item here : General FAQ & help
So for the scenes/actors file size to increase, it’s normal, it will go back down after a few operations happen or the next time you restart the server. The real worry is when it keeps growing exponentially. I don’t think you have to worry. The real issue is when some people have 500MB or even 1GB of data in their world (yes, I’ve seen that too often unfortunately, due to some modules spewing corrupted data in their database files), or if you have a very large number of entities (I’ve seen some with 200 scenes, 2000 actors, 10000 items) and end up with a 60MB actors.db for example. You’re at 5MB, so you’re totally fine.
Now the real question is, other than your worry and keeping an eye on the world scene, do you have any actual issues that you need fixed? You mentioned lags, so perhaps the issue worth looking into is why you have lag problems, rather than focusing on the world size, because I don’t think that’s your problem.