Yeah the FPS feels really low in the towns. Saint Denis feels the worst like 15 FPS...
If I remember right, they had this same issue in RDR1 and removed some of the people in the towns to smooth the FPS.
They would have to remove people, or maybe even remove the dust effects, or even lower the resolution if they have to.
Graphic options in the menu would be nice to have so we could lower the activity in these towns.