Well, in all honest, it could be a little bit of both. 15 FPS sucks. The game defaults the graphics settings to the setting higher than medium, I believe. When in game, go into the display or graphics options and set it to medium low. Also, 2 GB RAM is pretty low as well, and could cause the game to run slower. 2 is the required specs, but recommended is 4. So try to turn down the graphics settings, and it doesn't hurt to turn off shadows or something else small like the black outlines of champions. If it has been hard from the beginning, it's likely related to your specs. So try that and let me know how it goes.