I've been playing this game since 2012 and the FPS issues have always been a plague to me. Initially, I thought the issue was with the laptop I was using at the time - a pretty crappy laptop I used mostly for work, it had an integrated Intel HD3000 card.
About a year later I bought a 2nd hand PC with a GTS 450, 12 gigs of RAM and a 2nd gen i5 processor. The game's performance improved drastically of course but the game would still dip in FPS when infected spawn sometimes etc. I've since upgraded that PC to have a GTX 1050 TI and a water cooling system and surprise surprise - the game still runs like shit. And quite recently Chrome has dropped Flash and the game no longer runs on Chrome, I've switched over the Firefox. It still runs pretty bad, and arguably it has more issues than it had with Chrome previously.
I just started this discussion to get a general idea of how the game runs for other people and how powerful (or weak) their computers are and whether they've just gotten used to the game running so poorly or if it's never been an issue for them.