Version bump for 0.15.0 release (#1832)

Author: mattdangerw

keras_nlp/src/version_utils.py

@@ -15,7 +15,7 @@
 from keras_nlp.src.api_export import keras_nlp_export
 
 # Unique source of truth for the version number.
-__version__ = "0.15.0.dev1"
+__version__ = "0.15.0"
 
 
 @keras_nlp_export("keras_nlp.version")