The more light sources you have/the brighter/stronger the light source is, you’ll have to render at higher samples (I’d say try 5000+) if you don’t want to compromise quality by reducing the amount of bounces, reflections, resolution, and so on.
Speaking of which, what resolution are you rendering at?
P.s. The parking lot I made in this post I rendered at 7000 samples because less caused noise to show wherever the lights where hitting. And this was rendered only at 1920x1200, 100% scale. I could of also fixed the noise by deleting a few light sources and making the ones I had brighter, or decreasing the resolution, but I didn’t want to compromise quality. Took like two hours to render 
I guess this is why commercial rendering companies exist xD.