Update RELEASE_NOTES.md for 1.5.15 release (#246)

Author: Arkatufus

RELEASE_NOTES.md

@@ -1,5 +1,7 @@
-### 1.5.14 January 23 2024 ###
+### 1.5.15 January 29 2024 ###
 
+* [Update Akka.NET to v1.5.15](https://github.com/akkadotnet/akka.net/releases/tag/1.5.15)
+* [Update Akka.Hosting to 1.5.15](https://github.com/akkadotnet/Akka.Hosting/releases/tag/1.5.15)
 * Allow all 8.x major versions of Npgsql
 
 ### 1.5.13 October 4 2023 ###

src/Directory.Packages.props

@@ -6,7 +6,7 @@
 
     <!-- Install from version 5.0.11 included all the way up to 8.x.x, but don't go up a major version -->
     <PostgresLowVersion>5.0.11</PostgresLowVersion>
-    <PostgresHighVersion>9</PostgresHighVersion>
+    <PostgresHighVersion>8</PostgresHighVersion>
     <PostgresVersion>[$(PostgresLowVersion), $(PostgresHighVersion))</PostgresVersion>
   </PropertyGroup>