Am I able to use UE with Visual Studio Express 2015?
To be short, yes !
You can even us your own IDE if you want, as soon as you use the Visual Studio 2015 (v140) tool chain, you can use whatever you want (even Bloc-notes ! Would be challenging to do so though :-D)
However, I suggess you use Visual Studio Community version instead of Express.
Have fun with Unreal Engine