Linux here, opened a folder with less than 3k loc in all files combined. It is currently in the background (smart mode is disabled), FF in the foreground. KDE system monitor is reporting 3%-5% CPU usage and 946,272K of memory usage. Also, if I move the window, my mouse becomes sluggish for about a second afterwards.
By comparison, the exact same folder open in Sublime is using 789,236K of memory (most of which is likely cached from the indexer + LSP plugin which has accumulated over the past few days), and no CPU usage.
Obviously this is an early preview, so it's not a fair comparison at all. I'm really excited for this though, as it's certainly very promising right now.