All of the burners go very low. The difference in the upper end of the BTU range is determined by the number of gas holes in each burner. The more holes, the more BTUs. The simmer burner has holes only around the inner ring, the 15K has holes around the center and out on the star, and the 22K has holes around the center and double holes out on the star.

The simmer burner is not underpowered at all. I think it goes up to 9k? Does anyone recall? I have used it to boil water in 1 qt pots, and to saute in 6" skillets and it gives off plenty of heat on high! It's use is not limited to simmering things.

I don't think you'd want to give up the simmer burner entirely because the smaller flame pattern is perfect for small pots.

The simmer burner is not underpowered at all. I think it goes up to 9k? Does anyone recall?

It's rated at 10k -- courtesy of the little sticker located under the left side grate rail...

As alku has said, it is not a simmer burner, but just a physically smaller burner. It's great for smaller, like 1 quart, pots and pans.

I don't think they can upgrade to eliminate the small burner. Each range has a maximum BTU output that cannot be exceeded for safety regulation (UL) reasons.

Even if you could upgrade it, I would not recommend it. Small pots and pans work so well. It is my primary burner for cooking small quantities of rice, heating sauces etc. Very useful, and plenty of power for boiling 2-3 litres of water at a time.