questions about RDS CALs

Hi,

We have a ML310E GEN8 HP server with Windows Server 2012 Foundation and we need to connect at least 15 devices by remote desktop (RDS).

My questions are:

1. It is possible that in a few months we change the server by one more powerful, if we buy RDS CALs for server 2012 can later transfer to a server 2012 R2 or even server 2016?

2. Windows Server 2012 Foundation only supports up to 15 users (15 CALs), I wonder if it supports 20 RDS CALs or are also only 15 supported.

Regards