Well, well, I took the same trip with the same airline but to Hanoi this summer [;)]
I’ve flown Cathay several times—the best economy experience I know on their A350s. Their A330 for HK-Hanoi was a bit dated, though, but it was a short flight.
And Hong Kong Airport is super well organized. A connection can be done in 30 minutes.
All that to say, 1h15 is totally doable. If you miss your connection due to a delay on the first Cathay flight, they’ll put you on the next one at their expense.
On the other hand, it’s better to miss the outbound flight than the return, since there are several HK-Ho Chi Minh City flights a day, but only two HK-Paris flights.
Have a great trip[;)]
Il n'y a pas de problème sans solution... et si il n'y a pas de solution, il n'y a pas de problème !