very slow update

gistfile1.txt

lines ~ 200k
levels ~ 20k

update
    lines
set
    level_id_upper = 
    (select level_id from levels
        where lines.atom=levels.atom and
            lines.ion=levels.ion and
            lines.e_upper=levels.energy and
            lines.g_upper=levels.g and
            lines.label_upper=levels.label),
    level_id_lower = 
    (select level_id from levels
        where lines.atom=levels.atom and
            lines.ion=levels.ion and
            lines.e_lower=levels.energy and
            lines.g_lower=levels.g and
            lines.label_lower=levels.label)