Are you running 1.6ST?
The data is kept. I upgraded my 1.6ST to 1.7 years ago (and have since pretty much kept up with the latest version since 1.10.)
I wrote an article about it at the time (back in 2013) that is available here:
https://tmib.net/how-to-upgrade-osticket-from-1-6st-to-1-7rc4/
As a side note you should be able to upgrade from 1.6ST to current (1.15.2) in one go. Please make sure that you back up your site and database before you start though. I haven't tried upgrading from 1.6ST in a really long time... but I've been told by the Devs that it should work.
As a side note the pre-requisites for running osTicket have changed a lot over the years. So you will need to upgrade your PHP and possibly your MySQL as well.
If you have any additional questions please do not hesitate to update this thread.