Start sbt like this:
SBT_OPTS="-Xms512M -Xmx1024M -Xss2M -XX:MaxMetaspaceSize=1024M" sbt
To run test against all versions of scala:
SBT_OPTS="-Xms512M -Xmx1024M -Xss2M -XX:MaxMetaspaceSize=1024M" sbt +test
To do full build and release to sonatype:
SBT_OPTS="-Xms512M -Xmx1024M -Xss2M -XX:MaxMetaspaceSize=1024M" sbt release