Are you on Windows or Linux? On windows 11 go to settings > power and battery > power mode and if you set it to high performance it almost doubles the TDP of the CPU. On windows 10 click the battery and drag the slider to high performance. If what I read online is correct the T14 and the T15 are the exact same heatsink and motherboard so unless the 1" gap from the end of the heatsink to the vent is that much of a problem they should perform exactly the same, just like the later T14 and T16 models. But 4 years is more than enough time for the thermal paste to be toast. My P1 ruined it’s paste in less than 6 months, but that’s also an i9.

But that’s the world of modern Intel CPUs. Turbo boost as far as you possibly can until you can’t turbo anymore. Then in 6 months when the thermal paste is ruined you’re searching for a new machine.