I have owned an EU3000is since 2001 and have used it to operate 3 different 15k air conditioners.
If you decide you need more power you can always add an EU2000i and run them parallel. This will work just like an EU2000i and an EU2000i companion. I do this at times and am able to run both of my air conditioner units at the same time. One is a 15K and the other is a 13.5k. As long as they don't try to start at the same time it works fine.
Honda doesn't advertise it but all or their EU units can be mixed and matched. You can even parallel three at a time.
