Are all the features on OS15.2 installed on my iPad?

Some iPadOS features may not be available for your iPad - as some require specific hardware that may not be present on your particular iPad model.

While I’m not aware of a published matrix - that explicitly maps available features to iPad models - the User Guide for iPad does identify software features that are restricted to some models.

The iPad User Guide is available both online using a web browser (such as Safari), or as an Apple Books download:

iPad User Guide - Apple Support

https://books.apple.com/book/id1567104892

If in Settings>General>About>Software Version... you see 15.2, it means that your device is currently running iPadOS 15.2, there's no way to install a partial version of iPadOS.

Regards

Giulio