I don't expect scientists to be sent in SZ-15 yet, after that who knows? Since TH-2 is already constructed, I think CNSA won't let it gather dust in the warehouse. My guess is once everything goes smoothly, it'd be launched before or around 2025. Once in six module configuration CSS can accommodate six crew stay, almost certainly scientists will be sent in every mission. But six crew stay may require next-gen spacecraft to be ready, which require 921 to be ready, so may have to wait till after 2025-2028. Unless they make up by using two SZ spacecraft.