Am I still visible to old contacts I have deleted long ago, when they intall whatsapp if they still have my number in their contacts? I've had my mobile number 15+ years and have used it for work purposes as well as private over this time, even though its my personal number. 

Could someone clarify - if anyone from the distant past who still had my number in their contacts then installed WhatsApp - would they now be able to see me in their WhatsApp contacts even though I deleted them as a contacts long before installing the App?
If they have your old number then they are still able to see your old profile.
You are not deleting your profile by simply uninstalling WhatsApp, you need to properly delete your profile by going into Settings-&gt;Account and select Delete my account.
Then your old profile is deleted and nobody will be able to see it or send any messages to it.