Ok, I'm not an electrican, but let me pretend for a minute that I am.
Let's assume the A/C was running flat out as hard as it can 24 hours/day. That's 15amps * 120 V = 1800 watts * 24 hours = 43.2 KWH per day. It can't draw more than that or it would trip the circuit breaker.
Your power converter is pulling several amps round the clock to run 12V systems and keep the battery charged. Let's assume 14KWH.
That would get you into the 55 KWH territory. But your A/C should not be running continuously, so it can't be drawing anywhere near 43.2 KWH.
I second the suggestion to shut everything off and see if the meter is still running, showing other loads. The turn on everything except the A/C unit and watch for a while to see what's going on. Finally, turn on the A/C.