The chances of PL-15 integration on the Block III seem to be high, according to Kaiser Tufail, who is a very reliable source. As for its effect on the J-10C, well let's put it this way: If I was a 3rd party buyer, I'd go with the J-10C, which has better payload and kinematic performance (and also better looks, which gets free points.) In fact, I've heard rumors that the PAF was still interested in acquiring a couple of squadrons of the J-10C, in addition to the Block III (although, this pandemic year may have effected that plan.)
As for export controls on the PL-15, that's up to China's discretion. Keep in mind though, that China has missiles exceeding the PL-15 already in development (e.g. PL-21/XX). These missiles may already be operational for all we know... Export controls are usually for top tier items, and the PL-15 is technically one level below that in China's arsenal. But again, it's up to China to do that cost/benefit analysis.