Yes, there is an entrance to Quintili from a side road that leads off to the left from Via Antica onto Via Nuovo.
Only discovered this last December after overshooting the bus south from Roma by one stop. And what a hairy time we had then attempting to negotiate the Nuovo and then the Antica on foot! Worst near-death experience I expect to endure in many a year.
Almost impossible to properly explore down there unless you have yr own car,
In Roma T.L.