It will probably be tough to find a pro bono lawyer, particularly for a 15 year old case where there will presumably be a great deal of work that must go into reviewing the case to determine whether there are any viable claims. As a threshold matter, the mechanisms you'd be dealing with are either a PCRA petition or a federal habeas petition. You'll likely have problems with both types of filings being deemed untimely so you will definitely need counsel to navigate the exceptions to the timeliness requirements. If you really are not in a position to get on a payment plan and have no ability to pay for a lawyer at all, you might want to consider the Pa chapter of the Innocence Project. http://www.innocenceprojectpa.org/. Good luck.
First you could try contacting the Innocence Project, although they tend to mostly take cases involving DNA evidence. You could also try filing a pro se motion asking fo a court appointed lawyer. You could also write to your local bar association and ask for attorneys who do pro bono, or, if not then would represent for a reduced fee. Finally, some of the larger law firms in Pennsylvania sometimes will tak these types of cases on pro bono. Find law firms with more than 500 lawyers, find their pro bono partner and write to him or her. Good luck.
You might want to contact the Innocence Project to see if they would possibly help out
The response above is not intended as legal advice. This response is for educational purposes only. I have not met with you and I am not knowledgeable about the specific details of your case. Each case is unique and different. Therefore, it is highly recommended that you contact and meet with a licensed criminal defense attorney to discuss your specific circumstances. In addition, an attorney-client relationship is not created by virtue of this response.