I will be arriving at "Don Mueang Airport at 12:15PM. What is the fastest way, using public transportation(not the shuttle, because my return flight isn't for 3 days),to Suvarnabhumi Airport and when can I expect to arrive there?

????????????.....Are you asking "what is the fastest connection btw Don Mueng airport and BKK?" Because you add your return flight isn't for "3 days"????????.

 

First off "What time of day is your flight from BKK?" if its at at 12:15 pm generally its about an hours drive.

 

Anyway Taxi's are generally the fastest but if you have some need for speed I'm guessing a Helicopter is faster!

On the assumption that the OP has ruled out using a taxi:

- bus # 29 to Morchit BTS Station (the first BTS station)

- then BTS to Phayathai Station

- then Airport Link train to Suwanaphum Airport

Total travel time, including waiting time: about 90 minutes.

                              A few yrs ago, I read a story (am not sure whether it's typical):  a small group of backpackers got a van from one airport to the other. The driver kept nodding off at the wheel, and driving erratically.  The backpackers tried to get him to pull over and let them out.  The driver wouldn't.  They got to the other airport without injury.

 

                        Be warned.  And be vigilant, and don't be shy about chastizing an <deleted> driver.  If I was on that van, and he wouldn't pull over to let me out, I might take drastic physical action, possibly even squeezing the back of his neck with my strong hand (I play guitar, so I have a tight grip).  I don't want any <deleted> driver threatening grave injury to me or anyone else.