Well that is one ballsed up patch for the PS4 version...let me explain...
Game as it was installed on Saturday was 18.74 GB and I played for 7 hours to mission 13 without any issues or noticeable bugs. Today a patch was released but my PS4, which only had 9.94 GB of free space, could not download it and I had to free some space on the hard drive. Puzzled as to why the patch needed 10 GB - surely it cannot be half the size of the game? - I proceeded to delete the 16.5 GB Skylanders Swap Force game but I was still told I needed another 123 MB!!! At that point I had almost 27 GB free on the drive. After deleting Mercenary King, the patch downloaded and it was 18.74 GB!
It looked as if the entire game had been redownloaded but not only that but the install size of the game had doubled in size to 36.5 GB; in other words the original game install is there and the patched version! What an utter waste of hard drive space. On the PC, with all the DLC installed, the game install is less than 11 GB!!! Absolute joke IMO; it must surely be a bug?