Did you run the execution file from the new command prompt? After changing the PATH environment, you need to open a new command prompt to reflect the PATH setting.
MATLAB R2015b has two versions for Windows, 32bit and 64bit. The execution file you have might be compiled with 32bit of MATLAB R2015b.
You can check the execution file is 32bit or 64bit as described the "The really simple way to check if a file is 32-bit or 64-bit" section in this link. Right click the execution file and go to "Properties". In "Compatibility" tab, check if Compatibility mode begins from Windows Vista (in this case, the execution file is 64bit) or begins from Windows XP (in this case, it is 32bit).
If the execution file is 32bit, could you try installing 32bit of MATLAB Runtime v90?