In the area you live you can easily have access to a running court ? a swimming pool ? a gym ? Whatever it is go for that and don't do galactic exercises do stamina exercise. For example if you go at the swimming pool dont do 50 meters sprint. Do 100 or 200 meters with small brakes. You don't need to go into muscul oriented exercise you need heart to work in high pace. In general improve your fitness. Good luck ,have fun, and im Jealous
Yeah, building in stamina is good.
But doing a FH stroke for few thousand times in a day is also different too.
I would suggestion that you train a few 6 hours days (3 hours in the morning and 3 hours in the afternoon) building up to your departure.
IE, every saturday for 1 months leading up to your trip.
Make sure its not just the hour but the intensity level too.
So with what Squareball mentioned - try and do 30 mins a day on jogging, long distance swimming etc.
Do your normal 15 hours a week - and the extra full day or two in a week.
This should come to 25 hours or so.
Then I think it should be fine.
When you in China, make sure you do enough stretches and cool downs.
Do it even when you wake up and before you go to sleep
First few days it may be tough, but after a week you will get used to it.
After two weeks to three weeks you may start getting tired
After 4 weeks of the same thing, you may start getting bored
So it all depends on how exiting the program is, and your attention level