Using old keyboard with new iMac

I just bought Mac mini M2 with my 2015 iMac 27" wireless Keyboard and trackpad. It works once in while and all of sudden stop working and arrow starts jumping around. I contacted Apple. They said buy a new one. For the smooth working environment, i will buy it.

yes, it should work fine.

It’ll work but it’s less secure. Your choice.

Outdated power-hogging hardware i.e. Bluetooth = less secure, more batteries. I would replace with new.

You're welcome.