Is a Mean Well RSP-320-15 a good choice for Top Charging?

Much depends on the batteries and their state of health.

If they are full charged they ' should' not be able to accept more than 21 amps.

One needs to know if there are loads on the batteries at this time too, or if they are disconnected from all possible loads.

I have run an 25 amp schumacher and my meanwell rsp-500-15 in parallel for ~65 amps. You can likely do the same with the Iota.

after the 15 minutes at 14.8v the iota will likely just drop out and do nothing while the meanwell takes over