It's amazing how much heat can be lost with the holders. If you've got a bit of hardwood ply, sandwich the workpiece between two bits of wood and then in the holder. It just keeps the heat in. Also, how thick is the solder because that can draw heat away as well. I use the same type mini blow lamp as you and I cut a 4inch length of the 1-1.5mm solder piece, drill a hole down the centre of a dowel handle and push the solder into that. Again, saves heat. You will char the dowel but, so what?
It will work, as will the paste, but clean, flux, I use the powder mixed to paste with water, and heat and then just touch with the solder, I normally dip the tip into the flux paste, and it will either go or not go. If not, it's not hot enough.
It can be a challenge but keep at it. You'll find you'll need it again and again.
Good Luck