Are there any straight converters that are programmable?
No, they are all mostly automatic. Most solar controllers will not program above 15V in bulk or absorb stage but will push higher voltage in the equalizer stage and some can be programmed to do that at short intervals. I'd suggest to review with the Mfg the optimal voltages and current for typical charging. That 15.3V is the highest I have ever heard for typical charge stages and would be problematic for some climates.
You can search in this section the various uses of the Meanwell power supplies used for getting higher voltage charges by certain users.
