I don' t know of any reason why you CAN' T shoot carbons from that bow. I personally shoot carbons from my Darton Viper, which is actually an older design than your PSE. In fact, the viper shoots those carbons just as quietly, and (for me) more accurately than the MQ 1 that I had last year.

The shop owner may be concerned about shooting very light carbons from an older design bow. Doing so may make the bow more noisy to shoot, and possibly more prone to damage.

Personally, I don' t think I would switch from those 2315' s the way they seem to shoot for you. JMHO.