In theory: yes
In practice: not sure
Given that your installation is more than 10 years old and there have been a series of major releases in between like LS 3.x, LS 5.x, LS 6.x and now the most recent LS 7.x, I think you will most probably run into some issues at one point.
If your system is currently in production, I would create a copy of the database and a copy of your installation and run updates on this version to check first in a test environment if everything still works. And you most probably can't go straight from LS 2.5 to LS 6.x or LS 7.x. You probably would need to go through LS 3.x, LS 5.x, LS6.x, etc. (I think LS 4.x can be skipped as it basically turned into LS5 if I recall right).
In any way, how many surveys and users to you currently have? Sometimes, after such a long time, a clean new install can be the better option. E.g. you need to have a look at which surveys you really still need (you can export them as LSS or LSA files and import them in a new installation).
I personally, depending on the number of current users and surveys of course, would probably favor the "clean install" and transferring what is necessary to the new installation. You could keep the old version running for a still a while as a legacy installation until everything has been moved to LS 6 or 7.
If you need to keep a lot of surveys or have a lot of active users, this might be quite a bit of work of course. But I feel like the chances to run into issues when upgrading from a over 10 year old piece of software to the current one, there is a good chance that you run into trouble, and be it only because of the PHP version requirements of each of them.
Help us to help you!
- Provide your LS version and where it is installed (own server, uni/employer, SaaS hosting, etc.).
- Always provide a LSS file (not LSQ or LSG).
Note: I answer at this forum in my spare time, I'm not a LimeSurvey GmbH employee.
