nudge .... go that way
keep a damp sponge close by to keep the soldering iron tip clean.
put a drop of solder on the silver part of the tip to "tin" the tip this will help the solder melt.
as you have a 15w iron with lead free solder you going to find the earth points on the board will "suck the heat" from the iron. so wait for your iron to get to its hottest flux the gnd point tin the point nice and quick re-flux then hold your wire on the point put the iron on both wire and test point and wait for it to melt (you may need to tap the soildering iron tip with a bit of solder to get it started)
and thats the hard point done
the other points will solder easer