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.