seems unlikely. unless you switched to the new file system or did some other upgrade in the process.
mojave’s focus was on security, locking down more of the file system away from malware and accidental user mistakes.
the sandboxes got their first big overhaul since they were introduced too — but i suspect it didn’t do much to improve performance.
but a clean reinstall usually gives the impression of a speed boost while the system is perfectly clean and free of old cache files and the crud that builds up.
and btw: aside from the challenges of installing on old hardware it’s been a largely problem-free upgrade for me. i’m the world’s biggest fan of dark mode (no sarcasm here — i really truly am) — so that alone was worth the price of admission. i give it a thumbs up 👍 and say, if you’ve got the hardware then go for it, it’s mostly upside.