Since your Ryobi has 2200W peak, we were able to find the model RYI2200. According to its specs, it has a running output power rating of 1,800 Watts. Some people run into issues with this. With a SoftStartRV unit installed, you'll be able to start the A/C reliably on most 2,000 Watt generators. However, since many 15kBTU A/Cs could draw in excess of 1,800 Watts, especially in very hot weather, the generator will not be able to keep the A/C running indefinitely.
This is not the fault of the SoftStartRV, but it often gets blamed because the customer cannot start the A/C at all without SoftStartRV So, the first time being able to run the A/C sustained is with SoftStartRV installed, which then gets blamed for any deficiency that the generator might have.