no other way, only conserving mana
use perpetual healing at 1 target or max 2, its costs double every additional target
if you use only on 1 target the manaregen in this time will be more than per. healing costs (do you have "holy advantage" rubies? 3rd grid right upper corner)
but cast on 6 players at same time = mana empty
in general perp. healing on tank + holy healing should be enough
if tank needs more however go for "refreshing light"
mana-reduction rubies "angelic grace" (1st grid up) are also important
divine prayer is only emergencyheal
for mercenary matron not the same logic applies than for normal players, she is a cheater