We gonna need the specs of the PC you're running these games on, because Bluestacks is not like an emulator. It's more of a virtual machine, and there are a lot of unusual requirements and even BIOS settings you gotta modify to get it working correctly.
Your CPU needs to be able to virtualize, meaning it either has to be Hyper-V, or AMD-V compatible. That means having an intel core i7 6850HQ or newer, just to get it at a good speed. Then, you need to make sure its turned on in the BIOS.
Learn how to enable virtualization in BIOS. Check your system, access BIOS settings & activate virtualization technology for enhanced performance & capabilities.
www.simplilearn.com
RAM has always been a big issue with Bluestacks, because you don't manually set how much RAM the phone you're simulating requires to run. The amount of RAM it needs fluctuates wildly, so you might want to add more of it to your system just in case. As far as I know, you gotta select the device its simulating through a list. The galaxy S6 is in the list somewhere, and it only has like, 3 GB of RAM in it. Any software that does virtualization will always need a ton of RAM.