There is a lot of people noting that is a limitation of the RDPWrapper library:
Here: https://github.com/stascorp/rdpwrap/issues/192 =
"I can confirm that the 15-18 connection limit is present, regardless of the amount of RAM installed"
and here: https://github.com/stascorp/rdpwrap/issues/531
"We created several W2k16s VMs from different builds, with or without Windows Update and always this limit of 16 sessions. We concluded that the limitation is built into the product as soon as it is installed.
We added the RDS roles and features and then restarted the server.
Our connection tests allowed us to open more than 25 simultaneous sessions, one session every 10 seconds.
Uninstalling RDS roles and features, and then restarting the server, will restore the 16-session limitation."
another link: https://github.com/stascorp/rdpwrap/issues/512
So the real solution for +15 connections is to install the RDS services on a windows server.
Is not a Vcloudpoint or Windows limitation, is a RDPRwrapper