"MBP extremely slow after SSD Upgrade. What's wrong with my mac?"に関する回答The internet had the answer for me. Apparently your startup disk setting is pointing to a disk that's no longer in your system. I'm guessing the OS can't find it and is waiting for it to spin up. It doesn't try the new SSD until a timeout occurs. Go to system preferences and set your Startup Disk setting to be the new disk and I'll bet that changes everything. It did for me.