Can you check your webserver/php logfiles as well? Fatal error should give you some more details on what is going wrong.
If you compare to owncloud, which version are you comparing to (9.0, 8.2, 8.1)? I suppose you run the same configuration.
Tuning your mysql-server can be a good idea, tuning-primer.sh is a nice script which gives you some advice about cache-settings. Regarding the upload performance: ownCloud Central.
But optimizing is a different thing, if you still get errors, you should handle them first. If you get file-locking problems, you should consider using redis (see documentation).