@montalex: Theoretically, yes, the fonts hack might be causing some slowdowns (as well as possibly some speedups, it goes both ways
).
Try using another font, and/or switching to one of the FT overrides if it's not already the case (bci & bci_new being the one closer to the default FW 3.x rendering).
FWIW, I'm not seeing anything overly awful on my own device (and it's sitting at > 1k2 items, with at least a third of that being collections), but then I'm mostly using my Touch these days, so YMMV
.
You might also want to take a look at top/htop over SSH, see if something's not stuck on a loop in the background.