15 pages is waaaay longer than the ones I generally see.
The cafcass report should state the factual stuff, names, ages, basic info about the parties and the children, then at least touch on each party's version of events and what they hope to achieve.
Then it will talk about the child's ascertainable wishes and feelings (for younger children this may be based on the child drawing pictures of the important adults in their lives etc, for older children, more verbal info).
It should also cover any police/ss/school issues.
Then it should specifically address a checklist of the child's emotional, social, educational and physical needs, and how they are best achieved.
Finally there should be a conclusion with a recommendation re. residence/contact/other aspects of the dispute.
tbf, I generally go straight for the conclusion whenever I get a cafcass report, and often the longer ones are just repeating themselves, so personally I'd rather see a short report which gets to the nub of the problem than 15 pages of waffle.