I guess this wouldn’t be a very high priority, but it seems that VS2015 projects generated by Projucer don’t upgrade correctly to build VS2017, in case you choose to oblige VS2017 when it asks you if you want to upgrade your projects to build with new toolset (v141) the first time you open your solution.
This is really easy to reproduce - for example, just try to build the Projucer itself after agreeing to upgrade to the new toolset and it won’t work (I guess the solution to build Projucer was also generated by the Projucer)
Looking deeper it seems that some references to the old toolset (v140) remain in the Projucer-generated .vcproj files. I guess there’s some incompatibility between what the Projucer generates and what VS2017 expects to see in VS2015 .vcproj files.
The current workaround is just to choose not to upgrade the toolset; note that to be able do that you need either VS2015 installed or to install the older VS2015 toolset component when installing VS2017.