FRANKFURT, Sept 15 (Reuters) - Euro zone real interest rates are puzzlingly low, European Central Bank board member Isabel Schnabel said on Wednesday, arguing that investors may be overestimating the impact of the Delta variant of the coronavirus on the economy. “The market may be overestimating the risks to the global growth outlook from the spread of the more contagious Delta variant,” she said. “Delta variant has many characteristics of a genuine supply-side shock, raising prices and lowering output,” she added. “But market analysts’ growth expectations suggest that this shock is widely perceived as being short-lived.” (Reporting by Balazs Koranyi; Editing by Kevin Liffey)