Your baby is the size of a 15 lb Thanksgiving turkey.
Just so there's no confusion...
Your baby (probably) does not weigh 15 lbs (6.8 kg) in week 40 of your pregnancy. Your baby is the size, as in length, of a turkey that is 15 lbs.
If however, your baby does weigh 15 lbs, then may your personal deity have mercy on your baby maker.
And just for the record...
In September of 1955, Carmelina Fedele of Aversa, Italy, gave birth to the biggest baby on record at 22 lb 8 oz (10.2 kg). (Source: Guinness World Records)