It's definitely the slowest, and by pretty significant margins. Those tests did, however, uncover bad default settings in JDK 14 on some machine sizes, which happened to be those Phoronix ran their benchmarks on: https://kstefanj.github.io/2020/04/16/g1-ootb-performance.ht... Those bad defaults are fixed in 15.

Moving away from 8 results in a significant saving in hardware/hosting costs for the vast majority of large applications.