The answer is going to lie in your inverter manual/specs and your battery
On the surface it sounds like your inverter should be OK - if it is rated for 2000 watts it should handle 1500 watts for an hour or so just fine but sometimes the marketing
people get involved and mark things in an optimistic manner. Just check your manual or spec sheet for the inverter and see what the continuous use rating is.
If you are putting 1500 watts into the water heater, plus some overhead for the inverter, your battery
voltage will likely be drawn down below 12 volts during this load. Optimistically 1500 watts divided by 12 volts is 125 Amps. The actual draw will likely be a bit more. Check your battery spec sheet to be sure they are OK with that kind of a continuous load for an appropriate time period.
I suspect you will be fine, but check it out.