I have one of the 13" versions of that laptop (with R7 2700u), which I use for Uni stuff. I haven’t tried UE4 with it.
I’d be surprised if the 15" isn’t a bit faster but I don’t think the experience will be that good.
I work at a consumer electronics store in the laptop/PC department and we have one of those on display, don’t buy one without looking at the screen (with power unplugged), it has probably the dimmest/hardest to see screen out of the ~30+ or so we have on display, even worse than some of those super budget laptops with 32GB of emmc and Celeron N3000 series CPUs.
The screen on the 13" is significantly better, but not amazing.
Also remember that with the AMD APU laptops system memory is shared between the CPU and GPU, unlike similarly priced i5 + MX150 (or similar) laptops.
HP didn’t bother designing a more robust cooling solution for APUs either, as far as I know this is the same for most if not all of the Ryzen based ultrabooks. So if you dislike hearing the fan going, don’t buy one. It doesn’t get hot in the lap due to the ridiculously low temperature throttling setup (lookup ryzen STAPM throttle), there may be ways around this to get a whole lot more performance and it’s also probably not as bad on the 15".
With that negative stuff out of the way, I do like my one, I tried all of the keyboards on the laptops we have on display (Lenovo, Apple, Microsoft, Acer, HP (and Omen), Dell (and Alienware), MSI) and it feels better to me than all of them except the Microsoft ones (Surface Book 2).
If I had the money I would have got a Surface Book 2 with dGPU, but I didn’t so I got what I thought was the next best thing.
I suspect the Intel based Envy with dGPU might have been a better buy (especially for UE4 type stuff), but you miss out on the sexy color of the Ryzen ones hahaha.
As a note, I have played The Witcher 3 on the laptop (I think medium settings? Don’t remember).