14 days is all they care about, doesn't matter if it was bought online or in-store. I suggest you do what I did and really search a bunch or stores, call a bunch, etc. I got lucky and eventually was able to exchange my 16GB 6+ for a 128GB 6+ but that was after A LOT of relentless searching, calling, going to stores, unsuccessful time standing on a line, etc...because of how scarce the stock of 6+'s is. Finally I talked to a manager and he hooked me up. Maybe they can do the same for you if you talk to one and explain your situation cause you don't have much time left before the 14 days is up.
Good luck! And idk why Apple makes 16GB phones cause it's like having no space at all.