This Enicar is a real Gem! A special and extremely rare bird! It is linked to the F1 race because it was on the wrist of Jim Clark, considered by lot of people as one of the best driver of history! I really like the fact that it has big eyes.
You also forget to say that the first version has a different case compressor (EPSA patent). The quality of your first version can simply not be compared with the more common second version even if it is also a great watch. The dial is just amazing and the applied logo seems to be a miror! A too cool small detail!
Considering prices i think that prices are very high on cool vintage watches because of internet (the world became smaller) and the offer is limited.
Also, regarding the quality and extremely rarity of this Enicar, i am not surprised to read that you were offered €15.000 for it. But even at that price you should keep it! Where would you find another one if you regret it???
Enjoy it in good health!