Most of the time Microsoft release online installers for all its new visual studio releases and later after few months they publish ISO installers. I don’t know why they used to follow such practices which is so annoying specially in places where internet speed is not good or consistent.
I am also among those who faced problems with these online installers every time and that is why I published an article last year to download Visual studio 2015 from its online installer exe and then install it offline anywhere. Here is that article and I am going to use same steps for Microsoft Visual Studio 15.
You can download online installer (web installer) exe of Microsoft Visual Studio 15 from here
After downloading copy download file vs_enterprise.exe, copy it to any folder on your computer like c:/VS15. Now open command prompt as administrator and move to your directory where you have copied. Type vs_enterprise.exe /Layout and press enter.
This will open a dialog to ask where you want to download installer file, so just select the folder you want and continue. It will start downloading Visual Studio 15 on your system in selected folder.
After download is complete you can use these offline installer files to install it anywhere.