Hi user26705 ,
I suggest you have a look in the FMP 15 Help File for
Differences between the runtime application and FileMaker Pro (FileMaker Pro Advanced)
You will read
The FileMaker runtime application is for single-user solutions. Therefore a runtime solution cannot be shared peer-to-peer over a network. To allow multiple users to access the same runtime solution, you must open the runtime solution in FileMaker Pro or FileMaker Server.
as well as other limitations. The last sentence can be confusing: it means to allow multiple users to access the solution, you must share the FielMaker file used to create the runtime with FMP or FMS.