You'd be going from a dual core with iGPU to a quad core with dGPU, so the performance bump will be substantial. Video editing applications can be resource intensive and utilize GPU acceleration as well as multiple cores effectively, that is where you'll notice the difference. Video streaming shouldn't really require a quad core.
Also, the 15" has 16GB RAM default now, so there's a good chance you'll be seeing benefits from added RAM depending on how much you have in your 13" (not to mention if you use the dGPU, you'll free up system RAM reserved by the iGPU).