2 a/c units on 1 gen?

Stagger the start up and yes. From Micro air site the watts run around 1500 with the soft start in place.

Doubtful.

Softstart only helps on startup surge, doesn't help on overall running wattage and that goes up as the temps increase..

Try running both on your gen as is, start one up wait a few seconds then start the second one.. Then see how long it is until your breaker trips.

Coleman lists their 13.5K Mach 3+ as drawing 12.8 amps (1540 watts) in moderate weather, or as much as 15.4 amps (1850 watts) in "desert" conditions.

Coleman lists their 15K Mach 15 as drawing 13.9 amps (1670 watts) in moderate weather, or as much as 16.0 amps (1920 watts) in "desert" conditions.

That's the continuous running wattage - not the startup surge.

I run my two on an Onan 5500w. I'm guessing you could run either of yours but not both.

Tend to agree, 5500 W will run two 15K ACs, but 3500 is questionable.
Try it and see what happens, make sure everything else is turned off or disconnected.

Try it. So long as voltage doesn't drop below 107 no damage will occur. Start the larger air conditioner first.

Probably yes...until the cord melts. As skibine showed, you are probably looking at 27-30amps in ideal conditions. A 30amp is rated for 24amps continuous load.

In really hot conditions, you may be luckier in that the breaker will pop.

1540 + 1670 = 3.2KW in moderate temperatures
1850 + 1920 = 3.8KW in desert temperatures

Generally, any time you're constantly running a generator at more than 80% of its rated continuous output, you're stressing it enough to significantly shorten its lifespan.

80% of 3.5KW is 2.8 KW.

Well the Genny in my rig was 5500 watts.. Occasionally tripped a breaker.

I think you are asking a lot.
Suggestion.. Someone mentioned "Till the cord melts"
Unless the Genny has high-current outlets Consider a bit of re-wire

Route the power lead (or extend it) to one of the A/C's to a box or compartment (I suggest a dedicated box but if you put it in a comnpartment make sure the unit is in a METAL box inside the compartment) where you put a 20 amp plug on the end 20 amp plugs look like this -- | (the -- part is the neutral blade. I left off the safety grounde) and run a 12ga line to the same box and a 5/20 outlet -| | or |- | (not sure w/o looking at one) The Neutral is "T" shaped)

Plug into outlet for original wiring
Unplug and use a 12 GA extension cord to 20 amp outlet on the Genny

IF RF has 30 amp cord..:

IF the Genny has a 30 amp 240 volt outlet.... (Some do) Build a "break out" box
As follows
Two outlets One TT-30 one 15/20 Duplex (T-shaped neutral)
Safety ground (likely not connected internaly so you may need to connect it to Neutral lead.. I leave this decision to you)

Neutral lead goes to BOTH neutral Terminals

One HOT leg goes to the TT-30 the other to the twin 15/20

Plug RV primary into TT-30 Plug 2nd A/C into 15/20

OR..

IF RV has 50 amp cord.

Adapt from Twist Lock (Normal on such Generators)
To 50 amp RV outlet (you can buy that one at many RV or Generator stores)