WP15 bees constitute a whole, i.e. they integrate, in all its meanings. They take care of completing a whole with the future components.
What whole? The HL-LHC. How? By coordinating and deciding how to integrate the various technical equipment, intended to be installed in the accelerator.
These bees are also in charge of ensuring the harmony between the different engineering choices and the HL-LHC, always keeping in mind the technical objectives, the schedule and the cost.