There are other health effects than heart issues examined here - e.g. there's cancer, which occurs due to changes in the DNA of your cells, and that is a cumulative process (although e.g. outer skin layers replenish so in 15 years not the same cells, but I am not sure how long lung and other cells take to similarly replenish).

One cig every 15 years would be less than all the second hand smoking and air particles you digest.

But "less than 1 or 2 packs a day" sounds it will definitely lead to health issues. I'd say 1 cig a day would be acceptable and probably without serious health issues.