This comes from the Sims 3 twitter feed, but if you want an additional 15% off Origin, you can use the code ORIGIN15 to get it.
Here is the twitter feed (comes from the Sims 3 site)
https://twitter.com/thesims3The specific picture in question:
https://twitter.com/TheSims3/status/417735212231974912/photo/1I don't know if there is a specific time limit, or when it expires (thoughtfrom the message, probably New Year's Day), but if you are going to do some more Origins buying, it looks like it is still valid.
I can't confirm whether it will work on one of the items already on sale (seeing as how I already own all the expansion/stuff packs I can't test it). However, if someone is going to buy something on Origin (even non Sims 3), it should give you an extra 15% off
