Try shutting down your computer and re-booting.
Then Launch Creative Cloud
Allow CC to update first in order to refresh
Then go to the Apps Tab and the Try button should change to Install
If you need to update Photoshop CC or Photoshop CC 2014 do that first
Then click the install button for LR CC 2015
If re-booting doesn’t work immediately Launch Creative Cloud, click the settings (cogwheel icon) and sign-out from Preferences, then sign-in again.