I've just experienced this with the RTW release of 15.0.0+26228.9.

It's a mixed solution majority C++ with a couple of C# CLI projects (total approx 220 projects).

Every single time I start the build, via Build -> Build Solution, it takes over 120 seconds to start up the build process - i.e. doing anything at all and showing output in the Build window. This devenv process just seems to be sitting on CPU as various tools show there is no file access

In comparison, disabling the lightweight load means the build starts instantly, as seen in VS2015.

This issue has been fixed and is now available in our latest update. You can download the update via the in-product notification or from here: https://www.visualstudio.com/vs/ Thanks to everyone who provided feedback, votes and solutions for this problem.

Thank you for your feedback! This issue has been fixed and it's available in the latest update of Visual Studio 2017 RC. Thank you for helping us build a better Visual Studio!

Would be possible to know more details on the solution you experiment this problem? Are all the projects regular C# .NET projects? Did you measure your time on the first opening of the solution? When LSL is enabled there is a 'one-time' indexing happening that needs to be completed once and so the first build may be slower. But the second time should be faster. When doing a full rebuild the build time should be comparable with the regular solution mode if all the projects are supported. we are working on along term solution to make the gap not even noticeable.