Update CHANGELOG and library version for v3.15.3

Bug: 575975784
Change-Id: I0be658be941e4b32661ffe3d9977eafef3f3d1a8

CHANGELOG

diff --git a/CHANGELOG b/CHANGELOG
index dcaa449..8b27ccc 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -1,3 +1,12 @@
+2026-10-20 v3.15.3
+  This release is ABI compatible with the last release. See
+  https://aomedia.googlesource.com/aom/+log/v3.15.2..v3.15.3 for all the
+  commits in this release.
+
+  - Bug Fixes
+    * Bug oss-fuzz:572842743: Integer-overflow in
+      av1_choose_var_based_partitioning.
+
 2026-10-06 v3.15.2
   This release is ABI compatible with the last release. See
   https://aomedia.googlesource.com/aom/+log/v3.15.1..v3.15.2 for all the

CMakeLists.txt

diff --git a/CMakeLists.txt b/CMakeLists.txt
index aa17f68..92ee95c 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -23,7 +23,7 @@
 
 # VERSION is the release version of the library. It should be updated at the
 # same time as the LT_* variables.
-project(AOM LANGUAGES C CXX VERSION 3.15.2)
+project(AOM LANGUAGES C CXX VERSION 3.15.3)
 
 # GENERATED source property global visibility.
 if(POLICY CMP0118)
@@ -59,7 +59,7 @@
 #
 # The VERSION number in project() should be updated when these variables are.
 set(LT_CURRENT 18)
-set(LT_REVISION 2)
+set(LT_REVISION 3)
 set(LT_AGE 15)
 math(EXPR SO_VERSION "${LT_CURRENT} - ${LT_AGE}")
 set(SO_FILE_VERSION "${SO_VERSION}.${LT_AGE}.${LT_REVISION}")