And FYI, trying to plug them into different outlets in the same room will usually not help. Bedrooms are usually wired with a single 15A line.
Long extension cords are also a bad idea.
I highly recommend trying to lower the power usage, even if it means lower hash rates. You can also get higher efficiency power supplies which will decrease the overall heat generated and power used.
The best thing to do is to hire a professional electrician to put in 30A at 240V (or 208V if you have 3 phase). Higher voltages are slightly more efficient. A 30A 240V breaker can provide ~5700W (derated to 80%) safely. This is usually enough for 2-4 rigs, depending on their power usage.
All totally depends on who wired the house or even added on later. My living room alone has one wall on a 20a breaker, the opposite on another 20a breaker and the smallest wall has its own 20a breaker. Even most of my lighting is on their own 15a breaker....some are paired. If the house was built by a contractor and on the cheap budget then the whole room is probably on one breaker.
As many have said here.......To the OP........DO NOT CHANGE THE BREAKER TO HIGHER RATED BREAKER! And here is why.........
A circuit breakers two jobs in life is to PROTECT THE WIRING THAT IS HOOKED UP TO IT and protect a person from getting electrocuted because of a short to ground in an item that is plugged into its power circuit which ultimately also PROTECTS THE WIRING. The wiring in the wall is a certain gauge (size) and the breaker is sized by that. A 20a breaker protects 12ga wire. A 15a breaker protects 14ga wire. If you stick a 20a breaker on 14ga wire, you are allowing 5 more amps of current to flow through a wire thats only rated for 15a. The wire gets hot, the insulation of the wire gets soft and breaks down and when the wire starts glowing it will ignite the inside of the walls on fire. DO NOT DO THIS. All this applies to fuses too. Never stick a higher rated fuse in place of what it is suppose to be. A fuse pops and a breaker trips FOR A REASON.