I do agree myself that level 55 is a bit high for the combined song.
The combined heal / mana should probably be around 30-35 in my opinion, as this is right around the level range where bard starts to feel stagnant prior to the rework (i cannot judge post rework), and is right around a 20 level gap from when you get the individual songs.
I think by 45 we absolutely should have this song as this is when song slot economy is way overloaded and the regen effects are just too important. Other classes have already scaled into better healing, damage, tanking, etc by then as well; and heal/mana is kind of the bread and butter for the bard buffs. So getting 20-25% more effects for the group feels right.