You got lucky that the scene last week wasn't also incredibly slow. The low RAM warning is one that has to be taken seriously - at worst, speed can drop to about 10% of what it should be (as the CPU has to wait for data from the hard drive, which is much slower than waiting for data from the RAM), or in other cases can just outright crash.
32GB of RAM is considered a minimum these days, with 64GB being more of a sweet spot (though there are users who have even more than that, for sure), so a 16GB machine is going to struggle when the scene hits any sort of complexity. There should be a link in that message that you can click on which will give advice on optimizing the scene, though the preferred solution if budget allows is simply to add more RAM :)