Why is genymotion running so slowly?

The FAQ at https://www.genymotion.com/help/desktop/faq/ states

Several versions of VirtualBox are known to cause issues in Genymotion. For Genymotion to run properly, make sure you have the right version of VirtualBox installed:

Mac OS X: 5.0.26 (a sound issue prevents version 5.0.28 to run properly) Windows: 5.0.28 Linux: 5.0.28 In any case, do not use versions 5.1.x, as they are known to cause sound issues and in some cases prevent Genymotion to start.

My issue was running VirtualBox 5.1.x - I installed the recommended version and all was well again

From the FAQ:

Genymotion is based on virtualization. Make sure your CPU virtualization technology feature (Intel VT-x or AMD-V) is enabled in your computer motherboard BIOS.

Another option might be to increase the RAM allotted to your Genymotion device. You can click the "wrench" icon next to your virtual device in the list, and try doubling the RAM (e.g. 2048 => 4096). You can play around with it to find a value that works best for you and your computer.

I am using Genymotion on windows 10 to debug react native applications.

It didn't take 10 minutes to start, as described in the question, but everything was slow: took few seconds to refresh when I updated my code (and it was set to 'live reload'), took few seconds to respond to a click in an input field, etc.

Looking at the basic performance view of the task manager, the only parameter that looked problematic (close to 100%) was memory.

The emulator was defined with 4 GB memory (and 4 CPUs). I am using version 3.0.2 of genmyotion with virtual box 6.0.4.

I tried many things, and the only thing that helped was, unsurprisingly, increasing memory in my PC from 8 GB to 16 GB (it is a Dell Inspiron 3576 with i7-8550U CPU @ 1.80GHz[Cores 4]).With 16GB of memory I don't experience any performance issues (at lesat until the next Windows update :)