re: Maybe you forgot the decimal point
Are you sure it isn't $1.5 billion ? But maybe you're right and the price includes a new heavy-lift rocket, such as a modified shuttle ET with a base-mounted reusable shuttle main engine module, a nose-mounted CEV, and four SRBs ? But maybe it also includes a Moon base? After all, we're supposed to be going to the moon to stay.
The simplest explanation is that this is the cost amortized over the next 15 years.