I am going out once a day for a walk/jogging/bike tour. I am noticing that many do not comply with the minimum distance of 1,5m. Is there a real contamination risk if a person is closer, knowing that such a crossing between persons is relatively short?

The risk is very low in theory because outside, the contact period with the droplets exhaled by the person is very short.  This being said, in general, if you are not sure to be able to comply with the security distance of 1,5m, it is advised to wear a home-made mask (cfr. tuttos on the Net), as the other masks are aimed in priority to the healthcare professionals that really need them.