No, not all the cameras refresh in 15 seconds. If you watch them all on the one screen, as they first appear to you, you'll see which ones are changing on that occasion and which are not. Sometimes they are stopped for maintenance and so on.
Check the writing below each one. You will see which ones are static, by the time/date below it - as to when it last refreshed.
When the team is in there investigating, it will refresh, because they are there. When they have left, it usually becomes static on the last shot.
That's not a spirit. If that was actualy a spirit lady, the photo would have been around the globe 1000 times by now, as well as being on 60 minutes and Oprah. My guess, Its either one of the investigation team dressed in say a long raincoat/trenchcoat or its a Photoshop job.
Shame if it's a deliberate fake, because the old hospital has quite a bit of interesting activity if you have the patience, so it would be sick if someone turned it into a Photoshopped farce.