I did not use CATS but can tell you it took me a lot more than 15 hours per week.
A few examples of people I know.
Friend A. Studied part time after work weekends etc. using Bristol GS and completed first time passes in all subjects in less than 4 months.
Friend B. Studied full time at home using Bristol GS and completed with first time passes in 4 months.
Friend C. Started part time with some company that went bust, he had already sat and past some of them, changed school (CATS) got going again failed a couple, re-sat passed some more, ran out of time after passing 13, started again with CATS and passed them all in the end took about three years.
I have loads more examples but I'm sure you get the picture, I had to give myself a massive kick up the @rse! I'm glad I did.
If you are struggling getting going you have to make some changes to your life and be realistic, you need to cover the material and stop worrying about 15 hours a week or whatever! It will take what it takes
JL.................