i picked up a 1/2 gram of 15x at the very first week of september (2004) and we are now december. i wanted to save it until summer is it possible it will lose potency, or will it be just as good?
yes, salvinorin-A is a pretty stable compound, and it keeps for a long time. as long as you are storing the stuff in a dark, cool place, you should be just fine.
you are safe it keeps did you try it yet? 1/2 of 15x should be good for 40 sessions give or take efficiency of smokage. if you are hard headed you might have only 10 or 20 sessions. but it is a nice wee stash.
It may also help to put in a small drop of water into the bag (presuming it's IN a bag =P) to keep the dried leaves a little fresh, so they don't powder or dry too much.