I run Knots on an old laptop. I also run core on another (relatively new, low end laptop) for my BTCPay server. Both machines are with 8 gigs of RAM, and both took around 4-5 days to fully sync. Haven’t tried on a rpi, but a couple of people I’ve talked about trying to do a fresh IBD at 4 gigs told me it took them more than 10 days to finish over a decent internet connection.