I did run a Matrix server for a while. It continously consumed between 4 and 6 Gigabytes of RAM with about 5-10 users active at all times. Joining on of the larger rooms took 3 days, 2 days unil I didn't just receive plain errors and then another day until it would let me open the room without timeouting. While joining large room sit consumed almost all available CPU and several database connections for IO.

This was less than 3 months ago on a fresh install based on Docker with no modifications to the code other than instructed in the installation guide.