Prepare release 1.15.0 (#4522)

OpenTelemetry Java Bot · web-flow · commit b7779be1542a · 2022-06-10T10:58:49.000-05:00
diff --git a/version.gradle.kts b/version.gradle.kts
@@ -1,4 +1,4 @@
-val snapshot = true
+val snapshot = false
 
 allprojects {
   var ver = "1.15.0"
