GinFizz

First let's establish some terminology.
"Transit" usually means a connecting flight within 24 hours.
"Airside transit" means that to connect you do not pass immigration and stay airside.
A "stopover" is where you have a connection that lasts more than 24 hours and you enter the country, stay for some time and then fly on somewhere else.

Now the problem is this. Until the start of this month the only option to "transit" was via an airport with an airside testing facility. In that case you had to stay airside, take a PCR and antigen test airside, and then apply for the health code. Only a few airports had such a facility and only some of these were allowed to be used according to the Chinese regulations (for example it was possible at Arlanda in Sweden for some time, but after too many positive cases slipped though on flights to China, the Chinese authorities de-authorized the use of airside transit at Arlanda).

The new rules, starting from early in July are overall much more relaxed. BUT at least to my reading, they now exclude the use of any direct airside transit option, and instead request that passengers "transiting" follow the same requirements as for residents. This is a positive step as previously a health code would not be given unless you were a permanent resident in the country where you apply (or at the very least have been resident for 30 days).

The confusion here is that the Chinese embassy text refers to "transit" - whereas in fact the rules in fact now allow for transit via a stopover (where you enter the country and then are treated as if you were resident in that country - other than you have also to provide the health code from the country you first departed from)

So to my understanding, under these new rules, a 15 hour wait between flights is not going to be acceptable - though I invite others reading this to comment in case I have misunderstood the new situation.