By Kate Abnett BRUSSELS (Reuters) – A European Union proposal that member countries cut gas use by 15% to prepare for possible supply cuts from Russia is facing resistance from governments, throwing into doubt whether they will approve the emergency plan. The European Commission proposed on Wednesday that all 27 EU countries use 15% less gas from August to March compared with the average over the last five years. The target would be voluntary, but the EU could make it mandatory if Brussels declares a substantial risk of gas shortages. At a meeting of EU national diplomats on Wednesday, at leas…