High construction costs and a glut of product in the downtown market have caused developers to think twice. Between 10 and 15 proposed condo developments have been shelved or scaled back, according to real estate developers and brokers. Most loathe to admit it publicly, said Delores Conway, director of the Casden Real Estate Economics Forecast at the USC Lusk Center for Real Estate. “When you talk to the developers nobody wants to admit they are shelving it,” Conway said.