The battery is intentionally small, as it’s only intended to provide auxiliary power. Its primary role is to keep the vacuum pumps running for a short duration in the event of a power loss(e.g., engine stall).
Really? On what…? - Just being curious.
However, I don’t see any problem, and the 15A may be adjustable downward, either in configuration, or by cable selection - sometimes wire resistance is useful..
OK, so try it and see. Current can be limited by using relatively thin wire (1mm^2 is good for 15A), or by setting the charge voltage down a bit. hopefully the BMS will not cut off on exactly 15A charge current, but will have a small tolerance above this. The calls of the battery will also be able to cope with a little above C/2.