What's the latest version of Roslyn my analyzer can target if I support VS2015?

I'm writing a Roslyn diagnostic analyzer that should work on VS2015 and later editions. I want to know the latest version of Microsoft.CodeAnalysis I can use with my project and still support VS2015. I need to use an API that was added in Roslyn 1.2.0 (AnalysisContext.EnableConcurrentExecution), but I think that version of Roslyn isn't included with VS2015 (IIRC, only VS2017 supports C# 7). Does this mean I can't use this API in my analyzer?