Unfortunately there is no way to “speed up” this action – as stated by @Eric_Koleda in this topic: API delayed response - #23 by Eric_Koleda
You’ll see that you Coda module on Make returns a mutation id value, which you can further check to see if the request you sent to Coda is done or not – so no real time API here.
I would consider give a unique ID to each lead as it comes from your website and create a line on the Contact and Deal tables, with that ID. Then you could simply reference the contact on the deal table by it’s ID to create the relation between the two tables.