Is today the last day before Songkran closure or is the immigration office open tomorrow, i would imagine its going to be packed tommorrow with everyone trying to squeeze and extra day out of it if so? My visa expires on the 15th so i think ill have to go tomorrow for my 30 day extension

Immigration is open to morrow, but you can expect it to be packed. Open again on the 17th.

You could go on the 17th, the first day they are open again, but they might be even more packed. (No overstay fine if you permisison expires on a day immirgation is closed and you aply for an extension the first day they are open again).