Google is paying, and yes, you can, but they will disconnect you after a while. And if you abuse it too much, you won't be able to use it until the following day...
You can also buy Colab Pro and Colab Pro+, which have fewer limitations and faster GPUs.
In my usage Colab and Colab Pro were similar, with plain Colab occasionally OOMing during model loading. That said I've actually been seeing times slower than yours on Colab and I think they're slower than on my RTX 3080. ~15 secs per image. I'm not sure why, though.
You are much better off running it locally at those speeds. P100 does 13 to 33 seconds a batch in my experience. Cloud to cloud data transfer (Hugginface to Colab) is ridiculously fast tho.
I'm on Colab Pro and get about 3 steps per second when generating a single 512x512 image at a time, with slight throughput improvement when I batch 2-3 images
You can also buy Colab Pro and Colab Pro+, which have fewer limitations and faster GPUs.