② 15 minutes. Always fry two fish at a time. Don't leave the pot idle. First, fry one side of 1 and No.2 fish for 5 minutes, then fry the other side of 1 and No.3 fish for 5 minutes, and then fry the other side of No.2 and No.3 fish for 5 minutes. So it takes at least 15 minutes.
③495 minutes. Frying three fish is the most time-saving method. It takes 15 minutes to fry three fish, and 99 fish have 33, so 33 * 15 = 495 minutes.