I can't really tell. My computer is eight years old now, and it wasn't the best at that time, but can run the full game with all EP's and SP's (except Sweet Treats) plus quite a bit of CC. I have 32 GB of RAM though, for different games, as TS3 cannot use more than 3.7 GB (it still manages to fill up all those 32 GB with garbage after a while). I guess that means a minimum of 8 GB RAM, maybe more, would be advisable. I also have an SSD, which helps with load times. A dedicated video card is a must or at least advisable.
In principle, my computer wasn't set up for TS3, but for more modern games like Cities: Skylines, so I cannot really answer the question in good faith. I assume it's a common question in the Tech Help section though.