It's varied but generally speaking, in any 5- or 7-year period there's not going to be that huge a change up or down. You would be just as well served buying used copies (or a used set) from 2010 or 2009 or 2011 on
ebay for 1/2 or 1/3 of the cost of a brand new 2015 set. Look for the best price/most recent edition tradeoff and pounce.
Keep in mind that the vast majority of stamps in the 6-volume Scott set are going to be priced at .25 cents (or whatever the "floor" basic value now is). And that price simply reflects processing costs of these basic stamps.
Stamps valued at $.50 or $1.00 or even $10.00 may show some increases and decreases but even there the differentials are by definition minimal.
I have routinely compared 2005 with 2012 prices for a few dozen countries in the classic era and find that for classic British Commonwealth, there's quite often an increase of 20-30% for stamps that have catalogue values of say, $1.50 to 10.00 or 20.00. But for classic United states, including 19th earlies with cvs in the hundreds of dollars, prices generally declined by 10-20% between 2005 and 2012. That's very anecdotal but indicative. In many ways
ebay "concluded sales" searches for a given stamp or set give you a better, more realistic sense of prices than the catalogues. Catalogues are needed more for identifying and distinguishing stamps than for pricing.
If money is no problem, go ahead, get a new set but if you are looking for a way to finesse it, don't hesitate to go with a nice "late-model used version".