For the update 1.5 to 1.6 it is not relevant what you do first. But keep in mind that it is not possible to activate any changes correctly with a mixed version system. @r.sander already said “Do not activate any changes in between” 
For the update 1.5 to 1.6 it is not relevant what you do first. But keep in mind that it is not possible to activate any changes correctly with a mixed version system. @r.sander already said “Do not activate any changes in between”