The high amount of lights (not groups) indicate you might have used quite complicated geometry for the lights ?
In any case, this scene combines two complicated scenarios (lot of glossy surfaces in GI heavy environment for one, and lot's of lights for two). Both of those are tough to sample, but combined, yeah, nightmare.
I don't see as much fireflies as I see noise, and sometimes yes, 600+ passes (at default settings) it's simply what it takes.
HD success rate is also poor, but this can't be adjusted in any way currently but it's what simply happens in complicated scenes, I battle the same issues.
Also, you probably don't need portals, they're quite gimmicky imho in Corona and often that not, can complicate your situation. In scene like this, 99perc. of light is from inside, you don't need any portals.