Lag issues, unfortunately, are not likely to have anything to do with our servers and instead with how Valheim works. Our servers run underloaded and they are connected to one of the most well-peered providers in the world. You'll run into the same issues at any server host.
Valheim uses a unique Hybrid-P2P system for multiplayer not like any other game, the game is not actually run on the server but on one player's PC/console. When a new player enters a zone they become the "host" of that zone (or chunk), and all of the game logic (physics, enemies, chests, fighting, items, doors, etc.) is then run on that player's computer. The server just relays information - if another player performs an action it gets sent to the server, then to the host player, then back to the server, then to the player that performed it to confirm. This means that if the host player has a poor connection, is far away from the server, or has a slow computer every other player in the zone will see all sorts of lag, glitches, and even disconnects.
The only way to reduce the impact of this is to make sure the first player in a new zone has a very good connection to the server and a powerful system. You can usually ensure this by making less effective host players portal to a different zone and then come back, with the well-connected player staying put.
You can find more technical info on the Valheim Wiki
You can find your world files at this location on Windows
(You may need to move from cloud to local in-game first)
Paste this path into the "File Name" section of the window that appears when you choose your DB and FWL files and you should see all of your offline worlds.
Please remember that you must have both files, and that they must be for the same world. You can safely ignore any .db.old and .fwl.old files, they are not needed.
You can find your local V Rising save files at this location
From this path, open the folder with your SteamID, then v2, then your unique GUID (it will look something like e44b2230-54eb-4e1d-975c-cddd5eab4069) and inside you should see numbered AutoSave gz files. Upload the most recent one (for example AutoSave_99.save.gz).
You can also follow these instructions to upload a save from another server host, just use the most recent AutoSave file from the world you would like to upload.