I think some of server performace settings will reduce memory use
viewtopic.php?f=10&t=1825and you can make map load smaller area which should help memory
# The allowed adjustment range for the automatic rendering range adjustment.
# Set this to be equal to viewing range minimum to disable the auto-adjustment algorithm.
# type: int
# viewing_range_nodes_max = 160
# The allowed adjustment range for the automatic rendering range adjustment.
# Set this to be equal to viewing range maximum to disable the auto-adjustment algorithm.
# type: int
# viewing_range_nodes_min = 35
and probably best thing is to kill all programs you're not using on you computer while playing. auto update, virus scan ect.