Francis is a big boy, so give him some time to build some kind of tank. We have to be patient. It took Hurls 5 years to get to AA level. ( I reckon he got to that level about halfway through the 2014 season.)
And he's a growing boy which sine pointed out previously, I would also hope that things like Glandular fever and the like have been eliminated for his lack of endurance. Would hate to see him pushed into chronic fatigue. But hopefully totally jumping at shadows there.
The upside is that if he is growing still and is as talented as indicated, we could have stolen the best KP in the draft with a bit of luck.
So I'm with you Chris, just give the boy time and let him "grow" into his potential and start pushing when his body is ready for it.