Unless you have your problems refined to system training style uniformity: each one designed to target specific movements, then the more problems you do the more complete the workout will be.
If you do just one problem 15 times you risk injury because you will be stressing the same muscles in exactly the same way repeatedly, which works fine with weight training, but climbing moves haven't been refined for form in the same way that lifting weights has; in weight training you move the limb through it's normal plane of motion, in climbing you do whatever it takes to get the next hold.
The most structured way is to take a system training style approach: look for problems that have similar moves (undercuts, gastons, lock-offs, etc) and group them together, make sure that every arm position (for both L+R) is represented, and then do the same for grip types.
A less structured (less anal) approach is just to do a circuit of problems.