It's funny in reddit, they say its impossible to hit 1.5 million XP cap 4-5 hours. But it is doable on a double XP weekend and on a really long custom full XP / full progression match where match time is set higher and like 9999 tickets etc . . . AND it's one sided and the good / skilled / SUS side decides to let the game go on as long as possible.
Depending the sources, one says EA has it at 2.2 million XP and its a daily reset at a certain time. Another from EA chat says XP gain is unlimited but 1.5 million XP cap is a bug.
So I don't know. Because reddit and youtubers tend to get the news first but for accurate, not so, unless the quote official BF comms.