You need a solid CPU and GPU combo for this. What is your hardware specs?
The two 4K ray tracing renders I posted here are generated using an overclocked Intel Xeon E3-1231v3 (3.5/3.9GHz 4C/8T Haswell,) 32GB DDR3-1600 memory and Gigabyte GTX 1060 3GB Gaming G1 under macOS High Sierra.
The 3D view, regardless mode, doesn’t work well without a good GPU: it doesn’t work on my HPC workstation, which has dual Intel Xeon E5-2680 (2.7/3.5GHz 2x 8C/16T Sandy Bridge,) 128GB DDR3-1600 memory but an Sapphire R9 380 8GD5 OC graphics card.
It appeared to me that in order to run KiCad 5 smoothly, you need no less than a mid-tier 2016-2017 gaming PC.