Ahh, you were thinking you could apply it to the taxes owed on the capital gain? Sorry man, the IRS has you against the wall here.
Capital gains and losses are added together, and the tax rate is applied to that.
After I got my CPA license I worked about two years before leaving the field for a variety reasons, one of which is that I hate having to deliver bad news.
PDC is right, you have to think about whether any of those stocks has a chance of recovering more than 15%, if so it makes sense to keep them.
On the other hand you can only claim capital losses in excess of $3,000 over your capital gain. So if you don't expect to have any large capital gains expected in the future this may be the best chance to take the losses and remove the curse that turd stocks put on your portfolio