Big investment banks are facing their toughest test yet in the current 2015 Shared National Credit (SNC) review, months after regulators warned the banks that the quality of U.S. leveraged loans that they arranged was not as good as the banks claimed, sources said. Regulators met with banks earlier this year after monthly monitoring started in 2014 revealed that several deals that banks claimed were in “good standing” were riskier than recorded, four people with knowledge of the discussions said.