Two million points sounds like a lot of math, but I joined Khan Academy seven years ago so it's spread out over a long time. There have been long stretches where I forgot about it, but I keep coming back because it's a fun diversion. I've been working at it regularly for the past six months.
There is research that says learning a new language helps prevent dementia. Maths is a language of sorts. I hope it's doing the same job!