CB activity archive

For how long does communitybuilder activity plugin save the activities?

Imagine we have the website for 15 years.
Will it still have the 15 year old activities?

CB Activity keeps activity forever. There is no archiving functionality. There is cleanup functionality that you can configure within CB Activity > Parameters > Cleanup. There you can specify how long to keep activity (up to 6 years). Anything outside that 6 years is deleted from the database entirely. If you want archiving you'll need to implement that your self as you'll have to have it move those rows to a backup table.

Is it possible to change this 6 years into 15 years?
By changing a parameter in the code?

Is it possible to change this 6 years into 15 years?

Have added a feature ticket to implement a Custom parameter option so you can specify whatever you like (e.g. in your case -15 YEARS as would be in strtotime relative date format).

forge.joomlapolis.com/issues/6992

By changing a parameter in the code?

You'd just lose your changes anytime you updated CB Activity.