ALWAYS BACKUP YOUR DATABASE BEFORE MAKING ANY MAJOR CHANGES, ESPECIALLY AN UPGRADE!!!!!
You now have three choices:
Stay on 1.5.0
Start a completely new installation of kiwitrees 22.214.171.124, or at least a new empty database
Use the 1.5.0 database, change the files to kiwitrees 126.96.36.199 (remove 1.5 files except /data/ and replace with 188.8.131.52). I do not know what will work and what will be broken, but you will just have to hope we can help you fix it.