Judges refused to reduce the sentence yesterday but did agree to decrease the fine.
A Foreign Office spokesman said: "The result of the appeal hearing was given in Bulgaria today.
"The decision was made that the sentence will remain the same at 15 years in prison.
"The amount of the civil claim has been reduced from 200,000 lev (£70,000) to 120,000 (£42,000).
Michael's family intend to deliver petitions to Downing Street calling for more support from the government on November 30.
Labour MP Louise Ellman (Liverpool Riverside), who has been campaigning on behalf of Shields, said: "I am disappointed, but I am not surprised because the court did not hear any new evidence.
"It is crucially important that the court should question Mr Sankey and should also consider new evidence which is in the process of being sent out to Bulgaria."
The MP is planning to mount a debate in the House of Commons.
