Update changelogs from fern repo (#589)

Co-authored-by: fearthecowboy <[email protected]>

Author: fern-support

fern/products/sdks/overview/csharp/changelog/2025-08-25.mdx

@@ -1,3 +1,6 @@
+## 2.1.15
+**`(fix):`** Ensure dynamic snippet method calls can use literal values
+
 ## 2.1.14
 **`(fix):`** Create link in README.MD file to the REFERENCE.MD file