I’m not a Apple guy but maybe I can help.
Did you get any errors during install?
DVR 15 (as does all DVR versions) requires) PostgreSQL to be installed. My current version on my PC is 9.5. Can you check to see if PostgreSQL got installed?
If not, I would try to reinstall V14 as it should properly install SQL dbs.
Your uninstall of V14 may have uninstalled all the SQL stuff.
On my install of 15 Beta I did not uninstall 14 and it worked AOk.
As 15 is beta, all the install quirks make not have been fixed as yet.
ciao,
Ken