You know what they say, if it sounds too good to be true, it probably is. It seems, however, that you are able to take advantage of a loophole in the official Windows Upgrade Offer site to purchase Windows 8 Pro for just $15, never mind you purchased a Windows 7 PC before June 2nd of this year, while informing Microsoft otherwise. This has been tried and tested by some who have said that it works – basically, anyone is able to pick up Windows 8 at Microsoft’s promotional price, where it was originally meant for late Windows 7 adopters only.
Regardless of when you purchased your PC, just inform Microsoft that you bought a Windows 7 PC within the past two months. Should you select a date that is close to June 2nd, you will be prompted for the current Windows 7 key, so choose somewhere nearer to October and you won’t be prompted. The rest of the details can be found in the source link, so if you want to have a clear conscience, skip it, otherwise check it out. No idea on whether Microsoft will close this loophole though, but they have been duly informed.