Seems like you DO meet the requirement, strange... Oh ! yes i know the problem : windows 8 ??? Not great for game really. You should've done the free upgrade for windows 10 dude !
I fyou don't want to; maybe you could clean up your computer internally and externally ; dust and regisrty/temp files/ unused files, launch the game with as little other processes and set higher priority with task manager ?
Hope it helps :)