It’s possible, but not true 100% of the time. Laptops will work less hard to avoid overheating, so if you’re noticing your game being slow only when you’re overheating, it could help. On the other hand it’s possible that heat isn’t an issue, and the computer is just running the game as well as it can.
I actually used to use a gaming laptop and for me it really did help. The catch is that you have to fork over some cash for a really good fan and it does get pretty loud. However with it my laptop was always cool and gained a couple more frames on average instead of tanking when it got hot