Is there a way to customize PyGMT legend font size?

I'm trying to change the font size of the legend in this PyGMT program, but I can't seem to find how.

Here are the lines for the legend:

#read Seismic stations from txt file
ETNA=pd.read_csv("/Users/user/Desktop/PyGmt/ETNA.txt", sep='\s+')
fig.plot(x=ETNA.LONG, y=ETNA.LAT, style="i0.15c", fill='red', pen="gray", label='81 ETNA')

# Legend
fig.legend(position='g-2.6/32+w2.4/1.5',box='+gwhite+p1p+i', S=1.3)

Generally, the fontsize of all primary annotations can be adjusted in a pygmt.config() call by FONT_ANNOT_PRIMARY (see also here). To adjust the fontsize only within the legend you need to put the call into a with statement:

import pygmt

fig = pygmt.Figure()

fig.basemap(projection="x2c", region=[0, 7, 3, 7], frame=True)

fig.plot(
    data="@Table_5_11.txt",
    style="c0.40c",
    fill="lightgreen",
    pen="faint",
    label="Apples",
)
fig.plot(data="@Table_5_11.txt", pen="1.5p,gray", label="My lines")
fig.plot(data="@Table_5_11.txt", style="t0.40c", fill="orange", label="Oranges")

# adjust font size only for legend
with pygmt.config(FONT_ANNOT_PRIMARY="20p"):
    fig.legend(position="JTR+jTR+o0.2c", box="+gwhite+pblack")

fig.show()