One pitfall with the update from appliance firmware 1.4 to 1.5 is, you also need a compatible CMK version for 1.5.
As @aeckstein said the complete upgrade path that was done is now the important question.
normally i would do such an update this way
- upgrade appliance to the latest 1.4 version
- upgrade CMK to the latest available version on 1.4
- check if the same version is available for 1.5
- upgrade firmware to 1.5
- install CMK version for 1.5
- start the site
- check if all is running
- upgrade firmware to latest 1.6
- here no CMK upgrade is needed as 1.5 and 1.6 are compatible