There are quite a few tools that help migrate websites from Joomla 1.5 to 3.x and you can find most of them in the Joomla Extensions Directory at: https://extensions.joomla.org/tags/joomla-migration/
There are free tools such as J2XML which is excellent at transferring articles and some other items but the paid tools can usually do a bit more.
Not all of the tools help with third party extensions but SP Upgrade has been successful for me on around 40 or so Joomla 1.5 to 3.x migrations including migration of some third party extensions.
SP Upgrade apparently can help migrate Community Builder although I can't vouch for this personally.
SP Upgrade also helps with migrating users, sections, categories, articles, contacts, web links, news feeds, banners, menus, modules and images.
SP Upgrade is not free but will save you quite a bit of time even on a simple Joomla migration.
SP Upgrade Migration Procedure
There are official instructions but this is what works for me:
Pre Migration Tasks
- On Joomla 1.5: Empty Menu and Article Trash otherwise trashed articles are migrated too.
- On Joomla 1.5: Temporarily rename Categories under a Section with the same name as this confuses SP Upgrade.
- On Joomla 3.x: Install SP Upgrade component on your 3.x site just like any other component.
- On Joomla 3.x: Check in Global Configuration -> Server -> Database Settings that the database is set to MySQLi
- On Joomla 3.x: Delete any users, menu items, categories, articles, modules that might conflict with items being migrated.
- On Joomla 3.x: Empty menu, article, category and module trash by setting status to "Trashed" and click on "Empty Trash".
Set Migration Options
- Set and choose appropriate configuration, database and FTP settings at Components -> SP Upgrade -> Options.
- Choose what to transfer under the "Core Transfer" tab such as users, sections, categories, articles and so on.
- Click on "Transfer" to start.
- This can take a while depending on the size of your website. Progress is periodically updated.
- When migration is completed, save a copy of the log to your local machine for reference.
- If the migration times out, just go back and repeat the process. It will begin from where it left off.
Supported Third Party Extension Transfer
- In general, the process will be as follows but read and follow any instructions for the specific extension.
- Migrate core content before migrating extensions as core content may be a per-requisite in some cases.
- Repeat the migration process for each supported extension you wish to migrate.
- Before starting, upgrade to the latest version of the extension on the source website.
- Before starting, install the latest version of the extension on the target website.
- Select the extension you wish to migrate under the "Extensions Transfer" tab and click on "Transfer".
- Save the Log somewhere before you uninstall SP Upgrade!
- The Super Administrator account from the Joomla 1.5 account is migrated but with "v15" appended to the user name and email address.
- Log in with this old account, delete the Joomla 3.x Super Administrator account and rename the Joomla 1.5 account back to original. This preferred method retains the original user ID so that articles and Kunena posts etc. are associated with the correct administrator.
- The original Joomla 3.x /images folder may be backed up to /images_bkp_[date-time] and this folder can probably be deleted.
- Fix module positions to suit the Joomla 3.x template.
- In Menu Manager, select all menus and choose the "Rebuild" option.
- Test everything on the Joomla 3.x website to make sure it is working as expected.