I agree with other Answers posted on this Question, but none of them have answered the actual question in your title - namely, how to speed up the project (without harming your personal credibility). While this does seem somewhat of an XY problem, for this Answer I will take in good faith that this (and your personal credibility) really are your #1 (and #2) concerns - above such 'petty' concerns as quality or delivering value.
I can think of only one possible approach for this. Cut out scope.
Are you familiar with the concept of a minimum viable product (MVP)? Have you created one for your first iteration? Are you sure?
On an earlier project for which I was a Scrum Master/Developer, there were these two particular features. One was requested by a single user, and pushed forward by the boss as a 'must have'. The other was, as far as I can tell, requested by no one, but was also pushed through by the boss as a 'must have'. Both of these were also extremely complex, especially together, and interacted with the entire system.
Even after the features were coded in, we still pushed to remove them, purely because doing so would vastly simplify the system, thereby making any other work much easier/faster.
But instead, we went live with both features. And, years later, still no one actually uses them. Users actually complained about how one of these 'must have' features made the product too complicated and provided no value.
Removing functionalities that have already been coded has an initial cost, but may save you time in the long run simply due to reducing complexity. The only way to determine if you actually have such a feature, though, is to ask your developers. Essentially, ask them, 'are there any features that, including the extra time to take out and the reduced time to test, removing them would speed up the project?'
You then need to decide, for each feature the developers bring up, whether or not that feature is part of your MVP. If it's not - if it can be included in a later iteration (or never) and still have the first iteration be deemed acceptable - then cut the feature out of your first release.