15 hours, on your way to India, hmm... what about A Passage to India by E. M. Forster.

WBM2 is too dang big to carry, sorry Ralph!

The Herrigel book is thought-provoking, and compact. I reviewed it on Amazon and on here too I think, and it is definitely a must-read for photographers. But I doubt it'd take more than a couple hours to read, and it is rather academic.

What about Rites and Passages, about Minor White. You might like that.