Memory usage per session

Hi.
We have tested postgreSql,Oracle,MSSqlServer.
The test performs about 11K lines of code
Memory usage per session:
Oracle: about 5M
MSSqlServer: about 4M
postgreSql: about 160М
The result of postgreSql is very sad(Our typical business logic has about 30K lines of code).
How can I reduce memory consumption per session?
Note, we cant move the business logic to an application server as it will lead us to performance problem.

I can send the test script on request.

Test description:
PostgreSQL 9.5.3, compiled by Visual C build 1800, 64-bit
At the same time we run 50 sessions that perform the following functions:
CREATE OR REPLACE FUNCTION perfa.func9
...
BEGIN
svSql:='';
PERFORM perfb."func91"();
...
END;

CREATE OR REPLACE FUNCTION perfb.func91
...
BEGIN
PERFORM perfc."func911"();
...
END;

CREATE OR REPLACE FUNCTION perfc.func911 (
)
RETURNS void AS
$body$
DECLARE
svSql BIGINT;
BEGIN
svSql:=0;
...
svSql:=svSql+10;
END;
$body$