Comment 0 for bug 1498281

rc-proposed contains three versions of Mir: 0.15.1 + 0.14.1 + 0.13.3

$ dpkg -l | grep libmir
ii libmirclient-debug-extension1:armhf 0.15.1+15.04.20150903-0ubuntu1 armhf Display server for Ubuntu - optional client debug interfaces
ii libmirclient8:armhf 0.13.3+15.04.20150617-0ubuntu1 armhf Display server for Ubuntu - client library
ii libmirclient9:armhf 0.15.1+15.04.20150903-0ubuntu1 armhf Display server for Ubuntu - client library
ii libmircommon4:armhf 0.13.3+15.04.20150617-0ubuntu1 armhf Display server for Ubuntu - shared library
ii libmircommon5:armhf 0.15.1+15.04.20150903-0ubuntu1 armhf Display server for Ubuntu - shared library
ii libmirplatform9:armhf 0.15.1+15.04.20150903-0ubuntu1 armhf Display server for Ubuntu - platform library
ii libmirprotobuf0:armhf 0.14.1+15.04.20150821-0ubuntu1 armhf Display server for Ubuntu - RPC definitions
ii libmirprotobuf1:armhf 0.15.1+15.04.20150903-0ubuntu1 armhf Display server for Ubuntu - RPC definitions
ii libmirserver33:armhf 0.15.1+15.04.20150903-0ubuntu1 armhf Display server for Ubuntu - server library

It appears the main reason for the older packages still being present is platform-api depending on libmirclient8:

$ dpkg -s ubuntu-application-api2-touch
Package: ubuntu-application-api2-touch
Status: install ok installed
Priority: optional
Section: libs
Installed-Size: 361
Maintainer: Ubuntu Developers <email address hidden>
Architecture: armhf
Multi-Arch: same
Source: platform-api
Version: 2.9.0+15.04.20150326-0ubuntu1
Depends: libc6 (>= 2.17), libdbus-cpp4 (>= 2.0.0+14.04.20140310), libgcc1 (>= 1:4.4.0), libhybris-common1, libmirclient8 (>= 0.12.0+15.04.20150228), libstdc++6 (>= 4.9), libubuntu-location-service2, liburl-dispatcher1 (>= 0.1), libubuntu-application-api2 (= 2.9.0+15.04.20150326-0ubuntu1)
Pre-Depends: multiarch-support
Description: Implementation of the Platform API for Ubuntu Touch
 This package provides the implementation of the Platform API to
 bring up an Ubuntu Touch system.
Homepage: https://launchpad.net/platform-api