update v15 release notes

Author: AbanoubGhadban

docs/release-notes/15.0.0.md

@@ -11,15 +11,31 @@ Experience the future of React with full RSC integration in your Rails apps:
 - Enable powerful new patterns for data fetching
 - ⚡️ Requires React on Rails Pro - [See the full tutorial](https://www.shakacode.com/react-on-rails-pro/docs/react-server-components-tutorial)
 
-### Improved Component Hydration
+### 🚀 Major Performance Breakthrough: Early Hydration
 
-Major improvements to component and store hydration:
+**React on Rails now starts hydration even before the full page is loaded!** This revolutionary change delivers significant performance improvements across all pages:
+
+- **Eliminates Race Conditions**: No more waiting for full page load before hydration begins
+- **Faster Time-to-Interactive**: Components hydrate as soon as their server-rendered HTML reaches the client
+- **Streaming HTML Optimization**: Perfect for modern streaming responses - components hydrate in parallel with page streaming
+- **Async Script Safety**: Can use `async` scripts without fear of race conditions
+- **No More Defer Needed**: The previous need for `defer` to prevent race conditions has been eliminated
+
+This optimization is particularly impactful for:
+- **Streamed pages** where content loads progressively
+- **Large pages** with many components
+- **Slow network conditions** where every millisecond counts
+- **Modern web apps** requiring fast interactivity
+
+*Performance improvement visualization:*
+
+![Performance comparison showing early hydration improvement](https://github.com/user-attachments/assets/ae33fe14-42f1-4cc1-bde3-9c5bb570cdbf)
+
+*The image above demonstrates the dramatic performance improvement:*
+- **Left (Before)**: Hydration didn't start until the full page load completed, causing a huge delay before hydration
+- **Right (After)**: Hydration starts immediately as soon as components are available, without waiting for full page load
+- **Result**: Components now become interactive much faster, eliminating the previous race condition delays
 
-- Components and stores now hydrate immediately rather than waiting for page load
-- Enables faster hydration, especially beneficial for streamed pages
-- Components can hydrate before the page is fully streamed
-- Can use `async` scripts in the page with no fear of race condition
-- No need to use `defer` anymore
 
 ### Enhanced Script Loading Strategies