Supporting DirectX 11 is not an indicator of how powerful a GPU is, there have been DX11 GPU’s available for more than 10 years. When UE4 was originally released they had the GTX 660 as the minimum requirement, even with what’s available today, there isn’t an integrated Intel GPU that meets that requirement. So especially for him, the 2015 Macbook doesn’t come close to that. While the software might run, performance will be bad and likely would be too slow to be usable. There are some things that can be done to improve it though, like reducing the screen resolution, but I don’t know if it would help enough to make it usable.