The simulator tends to be pretty laggy, due to the fact it's an emulated device. It will run faster if you choose a simpler device for the simulator (iPhone 5, SE, etc.) but if your mac can't keep up there's not much to be done. If you want true performance levels your best bet is to just run it on the phone like pwrtoppl says. This is actually quite easy but you do require an apple developer subscription to load it onto a device, even for testing.