Use a semi-synthetic 10W40 from the manufacturer of your choice.
The thing to look for is the API rating... it's the letter after an "S".. so they are in the range SL, SM, SN, SO and so on.
Most semi synthetic oils are around "SM". The car manual probably specifies something as low as SG.. so any semi-synthetic oil you can buy will be several grades higher than this. I think it's impossible to buy SG oil these days.. even mineral Castrol GTX as Crabbo uses is "SL", I think.
Use the right grade, keep it topped up to MAX and change it every year and your motor will last forever.
Don't overlook "cheap" oils.. the Halfords (green bottle) semi-synth 10W40 has a higher rating than Castrol's Magnatec and you get 5ltrs for the price Castrol charge for 4.
I don't know why the manual suggests 15W40 mineral. It'll be thicker when cold than 10W40.. but not much. Use the thinnest oil your engine accepts.. 10W40.
Selenia is made by "FL" (formerly "Fiat Lubrificanti") but I think they are independent now (hence "FL"). Fiat sold it as part of their cost-cutting measures a couple of years ago, to pay for the new Punto.
Ralf S.