SecuritySuite - SuiteCRM and CE Teams

Hello, we have severe Performance Issues with the Security Suite and the following group structure: We have a Global Group (related to a Global role) and other Groups (related to another role) like: Sales, Marketing, IT, ... Every record (Accounts, Calls, ...) is related to the Global group and every record that is created is also related to the Global Group. For example if a record should be visible only for Marketing we remove the Global Group and add the Marketing Group to that record. Our securitygroups_records database table has now approximately 850 000 entries and the load of the server where the database is located is extremely high. The result is that our system can not be accessed. My Questions Would be: 1) how can we optimize security suite, so our system would run smoothly? 2) is our current group structure (replicated from Sugarcrm Pro) the cause of this performance issue? how should we change it for a better performance? Regards System: Suitecrm 7.2.2 (Sugar Version 6.5.20 (Build 1001))