It is a figure of speech. Literally, it would be: "leveraging the petabytes of data that we have".

In this context, if petatypes are not physical (I'm guessing it's a computer-related term) - "we sit on" is to physically have or an idiom for not making a decision yet. Im guessing petatypes is a noun. Then in this context, they are leveraging the petatypes that they have. In another context it can be used like this: For example, Brother 1: "Hi brother, have you decided where you're going to eat for dinner?" Brother 2: "I don't know yet. I'm still sitting on it." In regards to your comment, it's going to be literally having. "And so we built a model, leveraging the petabytes that we have, and we solved the tipping point."