For "A New Perspective", Is the total First-Person time calculated between Campaign and Online?
Solution 1:
From this Reddit post:
It accumulates between single player and online play overall, you don't need to play 15hrs in first person in one, continuous sitting.
You check it by going into your pause menu > Stats > General > Time played in first person (2nd one from the top).
You can confirm it yourself (as I did before posting this answer) by checking the menu that is mentioned in the second paragraph.