Hi,

In order to migrate a module from one version to another, you can try installing the module in the higher version and try installing it there.

Mostly there will be some trace backs on installation, if not consider you are lucky. So the trace backs has to be adjusted based on the error raised and continue till the module is getting installed without any issues.

Once installation is done, navigate to respective views to which changes are made and ensure no errors are thrown and do a functional test to see if everything is okay.

For technical changes in 15, you can refer this: https://github.com/OCA/maintainer-tools/wiki/Migration-to-version-15.0

For database migration:

1. For EE users, odoo migration service can be used

2. For CE, try openupgrade from OCA

Thanks