14.7 will not hurt your RV stuff at all. 15.4v is the limit for a Norcold fridge, eg.
Before buying, what exactly AGMs do you have? Each AGM has its own specs for charging voltages etc, so not all chargers can do some AGMs.
You can leave the 7455 in place and use a portable charger or mount a deck mount converter closer to the batteries if you have room, which would perhaps be easier.
Some (all?) AGMs want a 20% minimum amps recharge at least every so often, so 300AH is at least 60 amps for that, where that is amps at the battery not charger's rating.
I have 450AH of AGMs and with a 55 amp charger I have to split the bank and do batteries individually to get over 20% amps. AGMs can be a pain, but they do have advantages also.