I definitelly have seen this post-install load to atrshost on 2008.R2 also, so I'm almost sure this is not the 2012.R2 specific. It might be that something has been added to the post-install tasks that makes the load more visible.
On implementations with multiple processors and cores and with remote SQL this is not a big issue, but on VMwares with minimal HW settings such load might cause performance troubles for a while.
Thank you,
Alex.