There is a specific order in which you have to install the updates, did you save any of you reciepts from your old installation? If not, run through the updater in system prefs until the 10.1.5 is listed, then run the installer you are trying to use. If you did save your reciepts, then I believe you need to install security, updater, then OS... but I may be wrong... The easiest would be to just run through all the system updates until you get 10.1.5 in the list.