Zeokat imagine buy a new PC to update FireFox
Except you don't need to really buy it, at least not in the hardware sense. You can borrow/rent the power needed for those few minutes.
Options include running
composer update on a local PC with the same setup, or temporarily increasing resources on hostings that allow this kind of thing.
The memory-intensive task is just to compute the dependency between packages, which doesn't absolutely have to happen on the server itself. The challenge is that it has to happen in an identical environment (php version, php modules, ...) in order to download the correct dependencies. There are many solutions to run this task on a different machine, but none are super user friendly if you aren't familiar with Composer.
For now, the "official" solution is still to run Composer on the server itself and it likely won't change until we prepare the stable release.