java memory spring-boot

how to reduce spring boot memory usage?

I’m using spring boot to develop a client application.
and when run the spring boot application(using a fully executable jar), the memory usage is about 190M in x64 server, and 110M in x86 server.

My JVM options are (-Xmx64M -Xms64M -XX:MaxPermSize=64M -server),
why is it that in the x64 server, memory usage is so big?
how to reduce memory usage below 150M?