What dose of testosterone should be used to start the onset of puberty by ribcage expansion and shoulder widening in delayed puberty if testis is 15ml?

Varies: There are different preparations available, so it depends. For testosterone injections the dosing is 40-50 mg/m^2 monthly. Use 4-6 months. Dosing will vary depending on dose form, and these are just examples. Info per epocrates.

See your doctor: Please see your own doctor -- and/or an endocrinologist -- about your concerns. Trying to manipulate your own body with online or other testosterone could be dangerous to you.