Westend,
Indirectly other loads do affect breaker tripping on the roof air. Because they induce extra voltage drop. Then the amperage starts to climb on the air conditioner circuit.
It is a 15000 btu unit so it wants to be fed with great voltage.
The key may be "the first few hours". The compressor may be running flat out for all those hours (just as mine is right now). I find the wattage gradually climbs as one hour turns into five of constant running.
My own starts out at as little as 900 watts, but I've seen 1900, too (on a 13500 btu unit).
I 2nd the suggest of monitoring voltage.
If it is low then the OP may wish to investigate adding a plug in autoformer.
