[Veedrac]

Falcon Heavy is a huge outlier, and has never actually demonstrated the capability to lift close to its nameplate capacity to LEO. Falcon 9 is already volume constrained to LEO outside of Starlink or Dragon launches, and Starlink is packed incredibly densely to get to that point. When I ran the numbers some time back, New Glenn was similar to Falcon 9.

Increasing thrust by 15% doesn't just increase payload by 15%. I don't know a simpler way to estimate this than to run a simulation, and I don't have one with numbers I can toggle.

[adgjlsfhk1]

The really big change will be launch thrust to weight ratio. Going from ~1.2 to ~1.35 gives you 75% more thrust at launch which means you spend less time fighting gravity, less time in the thick parts of the atmosphere, and less time to get past the trans-sonic region.

[overfeed]

There are other constraints on how quick the vehicle should be, even when engine performance allows: you probably won't want to hit maximum dynamic pressure in too-thick air.