Importing XML files more than 58987 records per file (12 files queue)

Hi all,
Currently we have a Customer that needs his information from another System imported. All his information was given to us via XML files on which some are 76Mb or 100Mbs and number of Sales Invoices are 58,987.
At the moment was have a VM with 20MB Memory and 8 CPUs.
We are importing 3 files at the same time due to the time it takes to import… but still taking longer already a 1 week running and of course sometimes you get the Timeout Error … On Submit Lock wait timeout exceeded; try restarting transaction - #2 by luckyteam
And when the error is shown you have to start the file again… lucky the script will verify if records are created and only after will create missing ones.

Was looking at this [Performance] 1 Sales Invoice Save makes ~700+ DB calls. ~1000+ DB calls on Submit and wonder if on V12 changes were done to improve importing or submitting bulk files !!!

Any tips to improve our speed on importing those files and avoid or improve the Timeout Error is mostly welcome?

Thank you all