Doing this trophy requires you to complete 15 cooperative missions with other players. I did this online by talking to my accessory in my cell and selecting Cooperative requests. After connecting you can either look for rooms already made and if you do i recommend using the advanced search option to look for rooms at or lower than your CODE level.
If you don't want to join another room make your own! Host a lobby and set the settings to HOST picks operations only. I recommend doing CODE 2 level operation named CG2-3 Cloister Reach Objective. All you have to do is race to the end quick and easy! Do this 15 times with other players that join your lobby and you dont even need a full lobby. If your short some players and you start the operation AI will fill in the gap for you.
Now I'm pretty sure you can get this trophy doing invasion missions as well in the Cooperative lobby but thats nnot how i did it if anyone got it that way let me know!