Will this update slow down my iPad mini 2

From what I read at the time, the update was a minor point update, which provided security patches. It should not cause any issues if you update, but you should make sure you have enough free memory on your device, which is what often makes devices run slower.

Will what update slow down your iPad Mini 2? iOS 12.4.5 is the highest your iPad is capable of being update to. If you are asking about iPad OS 13, you'll need a newer device capable of running iPad OS.

I would recommend you to upgrade to a new iPad, since the iPad Mini 2 stopped receiving updates in 2019. If I were you I wouldn’t install iOS 13 on it.

iOS 12.4.7 is current for iPad Air1, iPad mini2 and mini3.

OKey Dokey. Perhaps I assumed the OP was asking about iPad OS 13. I'll keep in mind 12.4.7 going forward.

iOS 12.4.7 was not a feature update - but instead was a “point” update that addressed significant security issues.