First: I am no expert on this but do have an understanding of electricity from previous employment before retiring. Second, you didn't state whether you have two 13.5K units or the 15K units. For the purpose of calculations I used the 15K info. According to Dometic's charts the 15K units would require 13.3 amps to run the compressor and 2.0 amps for the fan. Those are "run" amp statings. The "start-up" amperage draws are much higher. Multiply this times two (2) units and you could have a total of 30.6 amps total just to run two (2) units. Dometic also states that you should have at least a 5000(5kW) generator to run these units, IF all conditions were optimal. You state that you have a 5500 kW (5.5kW) generator. That 5500kW is the manufacturer's stated watt rating. I've been around and used enough generators to state that those "manufacturer's ratings" are not always (seldom) accurate. IMO: Two 15kW units running at the same time could be putting enough load on your genny to cause the genny to shut down automatically then re-start automatically. Have you tried to run just one unit from the genny just to see what happens? You may have to find a place that can put a "load test" on your genny to see if will handle a 5500 watt load. Most shops that work on tractor-trailer truck rigs can do this. They have to test the genny's on the refrigerated trailers. Read this, it's interesting:
Sizing a Generator to Start Air Conditioner and Motors
Dual AC and generator
Linear Mode
