(doc) Removed JDK 15 from CI matrix

diff --git a/Jenkinsfile b/Jenkinsfile
index 1e77454..b4e13d9 100644
--- a/Jenkinsfile
+++ b/Jenkinsfile
@@ -17,4 +17,4 @@
  * under the License.
  */
 
-asfMavenTlpPlgnBuild(jdk:['8','11','15','16'])
+asfMavenTlpPlgnBuild(jdk:['8','11','16'])