Proper planning and knowing when to pull the trigger on upgrading PHP/MySQL in combo with the version of Moodle is key here. You are migrating and will be doing a 'march' ... upgrades to Moodle. Best to take things a step at a time.
Since the original server is still up and running, strongly suggest logging in there and go to Site Admin -> Server -> Environment. Then update the component.
Use the drop down pick list for version of Moodle and note what it says in the environment check ... for required versions ... of Moodle, of PHP + extensions, of MySQL server.
You can then plan your 'march' upwards after having cloned the moodle ... moodle code, moodledata directory, and a mysqldump of the database ... installed and up and running on the new Windows 2016 server. The DB will be a copy of the DB from 'production server'.
This new Windows 2016 instance will NOT be talking to nor should it attempt to talk to anything of the currently running Windows server.
Red Flags in postings ... 'depreciated errors' one cannot ignore. It means you are using a PHP that is too high for the version of Moodle code you have - which is the reason for the environment check and planning mentioned earlier.
The question about looking at the DB .... do NOT use the DB server that is being used for the running/functioning site. *Everything* in the new 2016 server to pointed to a clone of what you had on the functioning server.
The first step is to clone your moodle to another server and configure it to use it's new host. PHP and MySQL whatever are versions compatible with the 2.5.x code you have.
Get that working first. Then follow your plan for the 'march' and upgrading PHP/MySQL with DB changes at the appropriate time ... but not ahead!
At each successful step in the 'march' upwards, make sure you backup what you've gained in case the next step fails for some reason. If you backup, then you don't have to start over at the beginning of the 'march' again. :\
'spirit of sharing', Ken