Are you just having issue with playing GTA 5? Any other issues with broadband?
There's a lot of things you can try before you purchase more. Is it just stuttering? What laptop you got and what OS are you running? Do you have anything running in the background? Have you tried lowering the settings to see if that helps?
I don't play on PC but heard through the grapevine that 8gb ram isn't enough to play with max out settings.
Let us know how you get on or if you found a fix on other forums. ~CS~