A market research company is growing pessimistic about Illinois medical marijuana, telling investors that retail sales could reach just $15.6 million in 2016. California-based ArcView Market Research released its projections Monday. The estimate comes from the company's annual guide to legal marijuana markets, co-published with New Frontier. ArcView CEO Troy Dayton says some Illinois marijuana businesses will fail if the slow pace of patient approvals continues. Only 4,000 Illinois patients can buy the drug at licensed dispensaries. ArcView predicts the Illinois retail marijuana market will reach $23 million in 2017. The ArcView projections are much lower than a year ago for Illinois, in part because Gov. Bruce Rauner has not expanded the program to new health conditions such as post-traumatic stress disorder.