Should I download RU5 or RU6

Hello everyone , I have a questions would like to have your confirmation on this.

I have SEPM 12.1.6 MP3 and clients are 12.1.5. I have also set up LUA in the envoirement and is also downloading definitions for 12.1.6 . I have configured SEPM to download definations from LUA . Now I need to know the following.

1). Can SEP 12.1.5 client's download definations just fine from the SEPM 12.1 6 ( SEPM is downloading RU6 definations from LUA not 12.1.5 ) would it be any issue ?

2) I also want to enable a subset of 12.1.5 clients to get defs directly from LUA instead of SEPM . Now since LUA is downloading RU6 definations can clients use RU6 definations or I have to enable LUA to download RU5 definations as well since they cannot use RU5 definations ?

Thanks