Incorrect. The time for Arma to get the info from the database it needs and return back to itself is always the same. Whether the server has been up 5mins, or 4 hours. A few players or 90 players. This time is logged to call the database extension (the extDB DLL) and your data returned.
The database isn't the problem. It's the way the engine works, to deal with things. The queue can become long with a low server fps.
Take last night for example. There was some desync and it took ~30 s for me to get my database info and appear ingame. I ran a script to count how many dead bodies were on the map. There were 88! So I wrote a small line of script to delete them all and after that it was fine. Bodies may not clean up properly if people ALT + f4, as they don't run the clean up script when they click abort, to delete their dead body. This is made worse with a high turnover of players who join, then alt and f4 to quit.
For some reason, player clean up disconnect was changed in Altis Life some time ago. Before, it would loop through all dead bodies and delete them, upon a (proper) player disconnect. Hopefully, with all the big changes incoming for Altis Life, there will be a lot of improvement here.
The server can become slower to deal with things if it owns a lot of objects. It owns objects when a player disconnects. The body belongs to the server, your group, if empty, belongs to the server. Cars and many other objects for example. Again if there are a lot of players coming and going within a short time, they can give a lot of objects to the server.