Although Sonnet 15 does not directly refer to procreation, the single-minded urgings in the previous sonnets, may suggest to the reader that procreation is intended in the last line: "I engraft you new".
Sonnet 16 continues the thought and makes clear that engrafting refers to recreating the young man in "barren rhyme".
[2] They are referred to as the procreation sonnets because they encourage the young man they address to marry and father children.
The actual historical identity, if any, of the young man is a mystery; two candidates that have received the most consideration are Henry Wriothesley, 3rd Earl of Southampton; and William Herbert, 3rd Earl of Pembroke.
turns away from the theme of procreation and introduces a new and greater perspective, in which the speaker of the sonnets begins to express his own devotion to the young man.