Absolutely, the 15 is too small. With the IC15 you'd likely have to run your pump 24/7, and it might not even work at that in the middle of the hottest month(s). Some would even buy the IC60 so that they could run the pump even less. There have been some studies here about if using a 60 instead of a 40 ends up being a better deal: the 60 will need less runtime, and make more chlorine over it's lifespan, so it'll last longer, but it costs more... so how does that math compare to a 40, etc, etc. I worked it out once, I think the 60 was a slightly better deal, but not by much. My theory: Pentair did the same math and priced their SWGs accordingly, not so much by the material costs (just a theory). Buy at least the 40 and enjoy the ET control!