As we can observe from the comparison table of OCA/OCP8 exams, you are right that for the same 2.5 hours (150 minutes), OCA8 has 77 questions whereas OCP8 has 85 questions.
However, it does not imply that the questions in OCP8 will be shorter when compared to OCA8 questions. In fact, many questions in OCP8 we got were quite lengthy, sometimes spanning two pages (especially the ones with long code segments)! More number of questions to answer in less time does make the OCP8 exam more difficult to crack than OCA8 exam. In fact, we know many OCP8 exam takers struggle to manage their time and complete all the questions successfully. So, time management is an important factor to cracking the OCP8 exam.