Remember that pre-1900 rates of 2 - 4% were common. In WW2 in 1944, the top bracket was 94%. War is ridonculously expensive. Many caveats, but if 0% is not an option we should all want to see 1.5% rather than 15%.

15% still incentivises the use of accountants, inefficient reporting & corporate structures to shield themselves from paying. Sounds utopian, but the world would likely be a lot more peaceful and productive if it were single or decimal digits. People & companies would just pay and get on with building cool stuff.