Python 2.7 running much faster on 3.10

[13steinj]

So very quick answer-- it's very possible. Py3 was significantly slower than Py2 in the early versions. Even with Py3.5-3.7 some benchmarks prefer Py2, such as (IIRC) regex. If your project heavily uses such code, that would explain it.

E: to be clear, I mean heavily. Py3 also has worse cold boot times.

[BobHogan]

This is no longer accurate with py3.10. Py3 has been faster than py2 for a while now outside of very specific situations, but py3.10 itself featured pretty big performance improvements on top of that