A 15-year-old pleaded guilty Monday to first-degree murder in connection with a deadly October fire at a Lakewood apartment complex. The teen, whom The Post is not naming because he’s a juvenile, also pleaded guilty in Jefferson County court to first-degree arson, among other charges. The First Judicial district attorney in November charged the teen and a 12-year-old with first-degree murder and 39 other counts related to the Oct.