Fix Issue #55184 for Hacktoberfest - Update ocp-version attribute on main to 4.15

Author: rolfedh

_attributes/attributes-microshift.adoc

@@ -4,7 +4,7 @@
 :experimental:
 :imagesdir: images
 :OCP: OpenShift Container Platform
-:ocp-version: 4.14
+:ocp-version: 4.15
 :oc-first: pass:quotes[OpenShift CLI (`oc`)]
 :product-title-first: Red Hat build of MicroShift (MicroShift)
 :microshift-short: MicroShift