I'm confused. I thought it was your new MBP that's the slow one, or is the new one limited to only Internet problems?
Yes, just internet problems that seems to have gone away when I put the ISP DNS number back on top. Go figure.
As I recall, your old MBP is up to specs for Catalina, so the only thing I can think of at this point is to rerun the Catalina installer and subsequent updates if any...maybe on both MBPs?
And maybe even d/l the Catalina installer again before you do that.
