Is it true that flu shots only have a 1.5% chance of working as the doctors can only guess which flu will out break in any particular year?

About 75%, not 1.5%: No, not true. Judgment of strains to be covered in the vaccine each year is not always perfect, but it's not just a guess. Scientific analysis is involved and it's always much better than 1.5%. (Where did you see such a figure??) This year in the US, about 75% of potential cases are covered. (I don't know about Europe, however.) Get vaccinated. It can't hurt, and just might be life saving.