The following parameters should be set in order for Oracle to run effectively in a multi user environment.

Database Sessions and Processes

Increase the number of database sessions to 250 and the number of processes to 200.

sqlplus /nolog
SQL> show parameters sessions
SQL> alter system set sessions=250 scope=spfile;
SQL> show parameters processes
SQL> alter system set processes=200 scope=spfile;

restart the database.