There are two ways, both are used : "one point five billion" and "one and a half billion".
Another form for decimals (one and five-tenths) is seldom used for large numbers.
1,160,000,000 is one billion, one hundred and sixty million.
It is one billion one hundred sixty million.
One billion, one hundred sixty million
one billion sixty million
One hundred fifty-five billion.
15 billion
Fifteen.
Fifteen dollars.
Ten billion
15
15 billion is correct unless there is some reason to capitalize the word billion, perhaps in a title.
Those letters spell billion.
one thousand million=15 billion 1 billion/ 15 billion = 1/15= 0.0666
15
Eight billion, eighty-six million, nine hundred eight thousand, three hundred twelve.
Seventy billion