Writing to SQL server - too slow - excel

Question

I have an Excel sheet (using Excel version 1902) where i use VBA and an ADODB.connection (using Microsoft ActiveX Data objects 2.8 library) to read/write to an sql server (2016).
At first both the read/write operations were very slow, taking approximately 15 seconds each. There will be multiple read/write sessions so 15 seconds is not acceptable.
The amount of data to be read/written varies but is approximately 500 rows in 15 columns in total (split between 7 tables, so the number of rows and columns varies per table). In other words, the amount of data to be transferred is not massive.
At first I thought the problems was in my VBA code (loops, searching for text etc). But by removing those steps, I narrowed the problem down to moving through the recordset (.movenext row by row to read or write to the database).
For the read operation I managed to get acceptable speeds by doing the following:
Changed the CursorType from adOpenKeyset to adOpenForwardOnly
Changed the LockType from adLockOptimistic to adLockReadOnly
This reduced read times from 15 seconds to 5 seconds, which is acceptable.
However, I have not managed to achieve any improved speeds for the write operations which are still at 15 seconds.
I first tried:
Changed the CursorType from adOpenKeyset to adOpenStatic
Changed the LockType from adLockOptimistic to adLockBatchOptimistic
And then altered the .update command to .updatebatch.
I thought maybe that updating all in a batch would speed things up, but that did nothing.
Then I tried changing the connection .open statement from:
cn.Open "Provider = sqloledb;" & _
"Data Source=datasourcename;" & _
"Initial Catalog=catalogname;" & _
"User ID=UserIdname;"
etc. to:
cn.Open "Driver={SQL Server Native Client 11.0};" & _
"Server=servername;" & _
"Database=databasename;" & _
"Uid=UserIDname;"
Again that did nothing. With the updatebatch the native sql server connection performed worse (28 seconds) than the oledb connection. But with .update (no batch update) both connections were similar in performance at about 15 seconds.
Does anyone have any tips on how to possibly speed up the write operation ?