There may be 2 reasons for this:
1) Graphics card drivers are not installed.(This doesn't seem to be the problem here cause you say gta 5 works fine for you.)
2) It's the game engine to blame. This particular game lagged in my laptop too(4 gb graphics onboard) when I ramped up the settings.
And you might have noticed that game really starts to lag when rainfall occurs in the game. Try disabling rain feature if possible.
Have a good day.