docs: Fix release notes for 2.15.0 (#6315)

Co-authored-by: Caitlin Wheeless <[email protected]>

docs/source/guide/release_notes/onprem/2.15.0.md

@@ -41,9 +41,18 @@ Helm Chart version: 1.6.3
 
     ![Screenshot of warning message](/images/releases/2-15-performance-report.png)
 
-* There is a new Performance Score column on the project Members page. This score reflects overall performance, which includes annotations that were previously rejected and have since been accepted. This is different than the Review score, which only reflects the current accepted/rejected state of annotations. 
+* There is a new Performance Score column on the project Members page:
 
-    ![Screenshot of warning message](/images/releases/2-15-performance-score.png)
+    The Performance Score column reflects the overall performance of annotators. This score takes into account all review actions, including annotations that were initially rejected and later accepted. The calculation is as follows:
+    - Each annotation review action (accept, reject, fix+accept) contributes to the score.
+    - The score is calculated by summing the scores of all review actions and dividing by the total number of review actions.
+    For example:
+    - If an annotation is rejected twice and then accepted once, the Performance Score would be (0 + 0 + 1) / 3 = 33%.
+    - If an annotation is rejected once and then fixed+accepted with a score of 42%, the Performance Score would be (0 + 0.42) / 2 = 21%.
+
+    This is different from the Review Score, which only reflects the current accepted/rejected state of annotations.
+
+    ![Screenshot of performance score](/images/releases/2-15-performance-score.png)
 
 * There is now a link to the HumanSignal support portal available from the menu. You can find FAQ and troubleshooting information here, as well as a link to open a support ticket.