I try 2 GB instead of 10 GB and it help a bit. (It uses only around 1100 MB)
But it is still far from expected performance. Messages like
Can't keep up! Did the system time change, or is the server overloaded? Running 6294ms behind, skipping 125 tick(s)
still appearing multiple times per minute.
CPU usage is low, memory usage is low and no sign what could cause this.