Team performance may vary depending upon the nature of the project, team motivation, requirements, project management, methodology, or other factors. Project metrics are also dependent upon various factors. Out of the box, Redmine offers several metrics, which may be useful. Extended metrics can be achieved through plugins, third-party tools, or custom database queries. Improving team performance would require that you already have some performance record, then you analyze it, find bottlenecks, and work on methods to improve this record.
You will need Redmine to be used in production for a while to gain some data so you can use metrics. This period may vary depending upon the frequency of use of your Redmine installation.