I use LTspice on a laptop, and it is disturbing to make it go into high speed cooling fan mode. One thing you can do in LTspice is to limit the number of parallel threads that it will spawn. In the SPICE tab of the control panel, there is a "max threads" parameter that you can set. On a quad core Intel, the default will be set to eight, to allow you to use all 8 hypercores available from the Intel chip. If you're doing short simulations, then it's fine to leave it set to 8, but for simulations that take a relatively long time to converge or execute, I find it's helpful to scale "max threads" down to a lower value like 2. Modern Intel CPUs do clock boosting, and can also do core hopping, and this makes them very fast with single threaded applications. If you tell LTspice to only launch 2 threads, these can still hop among cores using a boosted clock while still avoiding thermal throttling, without burning up the chip. I haven't directly measured it, but reducing "max threads" from 8 to 2 seems to increase execution times a lot less than the factor of 4 that you'd expect, and makes long simulations much more practical, since the machine won't go into thermal throttling.
Laptops thermally throttle, and I find it's best to avoid that region to get better overall performance. Of course, depending upon the tricks your CPU can do, your mileage may vary.