Thanks a lot again, guys.
I lied. It's only 50 pops. The 51st is the pedestrian crossing the street, and he's a single object. Now, there's 50 pops, because I created five areas where people are walking. Each area contains five pops with offset animation loops walking in one direction and five pops in the opposite one. Unfortunately I hadn't thought of Kadri's idea to create masks at least for the identical pops that march in the same direction. It probably would have saved some RAM-usage, I guess. Apart from that there are eight pops with standing (Xoio-) people. See attached image (it's a PS-mix of RTP and regular preview).
Creating masks to avoid colliding instances would have been possible, but like that all the pedestrians would walk more or less in rows, which would look a bit unnatural. And think of all the obstacles: there are street lamps, bins, trash and canopied busstops. Each thing would have to be taken into account.