My current Non O expired Dec 13 , I arrived a Dec 3rd ,so I am enjoying my "bonus" 3 month . However after March 3rd I still need 2 weeks until my flight back to falang land .

Would like to do a land crossing to Laos . On return ,will I get a 30 day (EU Passport ) stay or only 2 weeks ?

You get 15 days for entering by land, 30 days by air.

Yes you would get 15 days.

What is your non-O based on?

If based on marriage you can get 60 days extension at immigrations for 1900 baht.

Yeah, there is a reason why you got that O visa, so yeah,60 day extension and go down the same route you went last itme