Depending from what initial GeneXus version to what target GeneXus version you are about to move, GeneXus does some conversion steps on your KB and you need to follow some particular steps too.
There is no KB conversion from 15 to 16.
More Information: GeneXus 16 Compatibility Section, GeneXus 16 is easy to adopt
From GeneXus 9 on, you can open any KB with GeneXus 16, and GeneXus will do an automatic conversion process on it.
Note that you don't need to open it with each intermediate version, but anyway check the following documents for particular points to take into account for your case:
For any conversion process, it is advisable to perform an objects navigation comparison.
Following you will find some conferences with information that may be useful in this conversion type.