Probably more than twice. The OCP covers more content and goes into more detail. Plus the topics and questions are tougher. So yes, it is way tougher.
I'd recommend to start reading and see how far you get. Even if you don't have enough time to pass the test, you already have the book and you do have time to start learning. Which will help at interviews and such.
Markedly more difficult. Many experienced developers can pass the OCA just by brushing up on the material and taking a few practice exams. For the OCP exam, I recommend a more rigorous course of study, as the topics are much broader and material more dense.