One thing to remember is that there is no magic number that is the parks max capacity. The actualy max capacity can change every day. There are a ton of factors that go into determining the max capacity for a given day. Some of the most obvious are the number of rides and restaurants open, and even the number of attractions running fastpass. That said 150,000 is way two high. However all four parks combines would be much higher than that. MK and Epcot combined would exceed 150,000.