@Anna *****************
I just checked with a service provider up north that bounces people out and back with Lao
They said you CAN exit/re-enter the border up there and get a new 15 day VOA for 2000baht but you would could be asked to meet the requirements (20K baht or the equivalent in CASH, proof of lodging for the 15 days, proof you're flying out in 15 days)
Good news is that you CAN do it, bad news is it's only another 15 day VOA for 2000baht