Is there any issue replacing a residential Eaton 15 amp type BRAF breaker (which is currently installed in a 15 year od panel), with Eaton's 15 amp type BR? I believe they are both AFCI's...
To be clear, an Eaton BRAF is a "Branch Feeder AFCI"
An Eaton BR is a plain old thermal magnetic breaker (not an AFCI at all.)
An Eaton BRCAF is a "Combination Type AFCI."
I see in your profile that you are under the 2008 NEC. That being true, in my opinion, the replacement breaker should be a BRCAF Combination Type.
There is no technical issue with installing the BRCAF, and, in fact, an increase in the level of protection occurs for the addition of "series" arc detection. The threshold of arc detection is lowered into the "running current" range for the branch circuit. The ground fault sensing component is largely unchanged.