When the --keepOriginalUrls option is used the framework is provisioned with Pax URL handler through an unversionned maven URL (ie. mvn:org.ops4j.pax.url/pax-url-assembly)
Even if the pax URL handler artifact is in the local M2 repository there is a communication to the remote repository to resolve the latest version. This slow down a lot the start of a fresh runner.
To have a startup with no communication with the remote repositories you need to have the pax URL handler artifacts in your M2 repository (not part of this issue) and the maven URL must specify the version of theses artifacts (ie. mvn:org.ops4j.pax.url/pax-url-assembly/1.1.2)