How did you do that, did you follow the tutorial?
(if you didn’t, there might be the old file path at a few locations, and then it might look for stuff that does not exist).
For the database, cache settings are important as well. Did you do anything in this respect:
https://docs.nextcloud.com/server/latest/admin_manual/configuration_database/linux_database_configuration.html#configuring-a-mysql-or-mariadb-database
(there are tools like mysqltuner, tuning-primer.sh that give tips regarding your specific use case).
Not sure if you have a lot of RAM, if you can cache many things, it should become much faster.
If a disk becomes slow, for long running setups, you also might consider that the disk has a problem (smartmontools).