Devkit has a lot of seriously big problems with some small parts of it. If it were open-sourced, it would be in a much healthier state.
@Memnarch, most VMs can be configured to consume x percent of system resources for the emulation. There is probably an error in that system (i.e, it is a fixed percent as default, meaning it will allocate way over the required amount of resources) That is a typical setup for an implementation of a virtual machine.
The slowdown can be explained maybe because allocating 81% of your ram forced a lot of application memory to be paged to your (I assume SSD driver because your computer sounds pretty bad ass)
Short, Herobrine has HPV.