How to set runtime version when calling C++ DLL from C++ app (Visual Studio 2015)?

[Quarter]

1) There are 32-bit and 64-bit versions of sharpsvn.dll, I use 64-bit.
2) The managed dll is 64-bit but it is not .net 2.0. As far as I understand there are different CLR versions, for example 2.0 (.Net 2.0 3.0 3.5) and 4 (.Net 4.0 4.5 etc). I supposed .Net 3.5 is enough - my VStudio 2008 solution is .Net 3.5 and is working with sharpsvn.dll properly.
3) Currently I don't know if sharpsvn.dll is COM enabled, haven't find such description. I've asked the developers about that.

As I see, if I add the parameter <startup useLegacyV2RuntimeActivationPolicy="true"/> to the App.config (in <configuration>) of the application using my C# dll - it starts working properly. The thing is that it works for c# app but I don't know how to set this parameter to the managed dll.

Currently I use managed dll built under VStudio 2008 with LoadLibrary - but using two versions seems to be rather strange.