You may want to calculate what happens when difficulty halves too, you know, for fun,  but that wont change the fact there is somewhere around 20PH thats been preordered and miners expect to come on line before february.

It will probably take longer than that, but even if none of those 28nm chips become reality over the next 100 days, BFL alone still has around 3PH worth of undelivered orders. and bitfury is not going away either (wouldnt even count asicminer and avalon out just yet). 

We just saw a dip in network speed, probably just random variation, but next difficulty is still projected to be +25% and thats before any of these new miners came online. 15% is a pipedream. You may as well calculate your winnings on satoshi dice based on the assumption you will have 5x more luck than average.