The annual January transfer window update has been issued for Football Manager 2015, and should automatically download and apply itself through Steam. If it doesn’t, try verifying your cache or restarting the Steam client.
This patch will be compatible with prior saved games if you want to continue on your current campaign, but in order for the database (and transfer) changes to take effect it would be necessary to start a brand new game. If you do that, all the exciting January transfers like … err … Yaya Sanogo being loaned to Palace? .. I’m sure there were some better ones. Possibly in other leagues.
As usual with a Football Manager 2015 patch, the match engine has had some tweaks. That means you should no longer encounter rather creepy sounding things like “Fixed bug where fifth official moves onto the pitch over the course of a match.” Keepers should be reacting to things a little bit more naturally by the sounds of the notes, too.
“Fixed bug making saves too difficult at certain heights and angles” and “Fixed keepers not punching balls they can’t hold at certain heights” atest to that.
There’s an extensive list of changes to be found on this page of the Football Manager 2015 forums.