Excel formula is:

=RATE(15,-40000,-100000,1500000)

you can also do positive 40k and 100k and negative 1.5m, as long as the signs are opposite - Excel assumes you're taking the $1.5m out immediately

Reb, the formula chimp gave is annuity due - so 40k was added at beginning of the period

OP, formula for that in excel is:

=RATE(15,-40000,-100000,1500000,1)