FTFY
Shorter springs = less suspension travel. Never really thought about this before, just always went along with the internet propagated 'knowledge'. Why would stock shocks last less time with shorter springs? Off the top of my head, there is really no reason for them to last less long unless they are bottoming out regularly in which case yes, you will ruin them. If you're not driving in quebec through craters every day and you're not so low as to be bottoming your shocks, they will last just as long as ever (which may not be very long if they are already old lol)
So, if the shocks aren't old, you're not driving on crap roads etc, there is no issue for the shocks, although the ride quality might not be as good because the shocks were carefully tuned to work with longer springs and using shorter springs will result in a harsher ride.
-edit-
That said, I am very happy with my prokit and yellows