This is referring to Front-End money and Back-End payments.
Example from ScriptMag.com
If you manage to sell a screenplay, you should receive at least $40,000 upfront and $75,000 on the back-end.
The front-end means the money you will get at the point of sale as soon as the deal closes. The back-end means the money that will be paid to you if and only if the project gets produced. Produced means when principal photography commences and the movie gets shot. The film does not have to be released for the writer to get paid. Once they shoot it, the screenwriter gets paid the back-end.
This is an example of how the front and back-end work. Let’s say you sell a screenplay and the deal is $40,000 against $75,000. You would receive $40,000 up front at the time of the sale, and receive another $35,000 if the movie goes into production. That’s a total of $75,000.
So in this instance, the character is saying they think they can get a high six-figure sum on the sale of their script, and then the rest (totalling $1.5m) if the films goes into production.