The structure of this financing is a bit convoluted.
Link to the SEC filing. And spoiler alert: This is NOT Rivian borrowing $15B.
First, this is all as a result of the Economic Development Agreement with these parties:
Rivian will actually rent the land and all buildings and machinery for the Georgia plant:
This will all be financed by a series of taxable bonds that the JDA issues:
So, wait, the company now buys the bonds from the JDA? So Rivian is actually financing the plant afterall.
So the JDA, as the bond issuer, pays interest and principle for the bonds to the bondholder, which is Rivian. And Rivian pays rental payments to the JDA to cover those same costs. So this paragraph above says that these payments cancel each other out and no monies are actually exchanged. The JDA doesn't actually pay interest on the bonds, and Rivian doesn't actually pay rent for the facilities.
The picture comes into focus. This bond crap is just a way for the state to secure its interests in case Rivian defaults on its employment and investment commitments to access the $1.5B tax relief package that was negotiated last year (I didn't excerpt the boring stuff about events in case of default).
Rivian isn't borrowing any money from this deal at all. Rivian will fund all plant construction and if they do what they committed to, they'll own all land, plant and machinery in the end for $100, and get $1.5B of tax relief. Actually, it is a bit more than just tax relief,
here's how that $1.5B shakes out: