If there dosent appear to be any trace of macKeeper, then should be fine. If still seams to be running slow, try the following:
1. Open Disk Utility and repair permissions
2. Open Finder and delete the following folder content:
3. See if Spotlight has finished indexing data ( spotlight could take a good few hour to index after installing the new OS)
4. boot into safe mode (hold down Shift when you start your mac until apple logo with a progress bar appears) after booting into OS restart your Mac.
AppZapper, and other apps like it, don't work all that well and can cause other problems. They will often miss stuff. If you don't know how to uninstall a particular application, rather than using something like AppZapper, you should Google it ("mac uninstall softwarename").
In the case of MacKeeper, see:
Note that, although many people refer to MacKeeper as malware, it actually is not. It is crap software made by a company that uses extremely unethical marketing practices, and should under no circumstances ever be used as certain functions (like the "cleaning" tools) can damage your system and even destroy personal data, but it's not actually malware.