I'm just saying that if you would rather have crappy resolution than spend $10 - $20 then more power to you. You only have as much noise as you are willing to put up with. If you don't want the noise then do something about it instead just accepting it laying down. There's two ways to do things , the half-assed way , and the right way. If you can't afford the ADC then that's another story , but if you can afford all that expensive RC crap (my garage is full of it) , then you can afford a lousy $10 or $20 ADC.
I's up to you You're only controling fans so it's not like it's mission critical or anything, but the way you presented your idea it sure
made it sound like everything revolved around sensing the CS. I just thought that it would be obvious that the response time of a PID or feedback loop would be a function of the precision (and sampling time) of the "sense" function. It's a trade off. The arduino can sample 10,000 times per second (10-bit resolution), while the ADS1115 can only sample 860 times /sec because it's 16-bit resolution. You have to decide what's more important, resolution or speed. You can't have both.