Hi,
GSA 6 is part of OpenVAS 8 which has reached its end-of-life a few months ago. Please update ASAP to the latest GVM-9 (end-of-life, initial release 2017-03-07) - Greenbone Community Edition - Greenbone Community Forum .
Unfortunately this is a question no one can answer you without having knowledge of / deep insights into your scanned environment. The amount of results for a scan highly depends on various factors like:
- exposed and identified services, applications
- existing vulnerabilities within this services/applications
- coverage of 1. and 2. within the used feed
- the chosen port list (e.g. All TCP vs. nmap top 1000) assigned to your task / target