I've heard some people talking about a redesigned combat system in 1.15, just wondering if this is true or not (don't have access to my pc at the moment, so I can't test it to be sure for the time being).
As of right now, 1.15 is the Buzzy Bee update which doesn't really change combat at all. There was a "Combat Test" update which was a fork of 1.14.3 that changed some combat mechanics, but none of those changes have been added into the 1.15 snapshots yet.
The 4th combat test was in 1.15 while the others were in 1.14.3 and 1.14.4 I think, but these are just snapshots Jeb makes to see what the community thinks, we don't know if it will be in 1.16 or never implemented (maybe even 1.17+) but we do know that 1.15 won't get the combat mechanic changes. If you want to try them out for yourself check out the reddit posts that have them (via Youtube videos that cover them or the MCForums posts on them).