Agree with others...no ap does not produce over attached children (disclaimer...in every walk of parenting there are folk who unknowingly bring their issues along in a major way and this affects their kids...ap isn't a cure all)
Ds is only 15m but will happily wonder off anywhere, go to other people etc.
He cries when i leave but settles quickly afterwards. This is a sign of a secure attachment. They would rather be with you, but it isn't the end of the world and they happily get on on when you're not there. This is worth remembering in relation to your ds. Though as others have said there may be something going on at nursery or it may be a matter of his personal preference etc like belgo's dd2.
Also he is more than happy to go off and leave me. I think the problem is more me going exploring and him not, as he see's it.
For me the underlying theme in ap is that you can not teach independance. You have to wait for it to appear. So as far as possible i aim for ds to signal what he needs. So i will bf, co sleep, sling etc untill he decides he's had enough. Then he can walk away having had his needs met.
Obviously this is not a criticism of you op, but would you consider co sleeping for longer with another dc? Clearly it isn't for everyone, i know it drives some people mad. But i also know that there is alot of pressure from the "rod for your own back" school to get dc's in their own bed asap. If you and a dc were happy with it it night be a pleasure for both of you. 
Tbh i from what you have said the problem seems to be more with other peoples comments. To me your ds sounds well withing the normal spectrum of behavior. 