Well, I don´t think there´s a standard answer for this question. In my opinion, the key its gonna be in how that or these posts add value to the user o help them. There is also important what type of keywords are you trying to reach (its difficulty). Assuming both options are made of good and helpful content, I would rather prefer having 10 long tail oriented posts of 1500 words instead of one mega post. It will mean more pages indexed and 10 times more chances to get traffic via Google.
Regards,
A
