can you please tell me if the update to the newer version of wallet is a mandatory action?
or it can be ignored?
cause it will convert blockchain or something like that? can I skip it and be on the old version?
It's not mandatory, but If you upgrade to new version, then you cannot go back to the old one without resync.
"
Downgrading warning
The chainstate database for this release is not compatible with previous
releases, so if you run 0.15 and then decide to switch back to any
older version, you will need to run the old release with the -reindex-chainstate
option to rebuild the chainstate data structures in the old format."