message: Update RELEASE_NOTES for 1.9.15
diff: @@ -5,8 +5,12 @@ A new header is inserted each time a *tag* is created.
  ## Next release (main branch)
  +## v1.9.16
  +
  ## v1.9.15
  +filamat / matc: fix sporatic crash.
  +
  ## v1.9.14
  - Improve bloom/emissive with glTF files.
  