No way 4 heavy weapons are healthy for optimal, even remotely competitive gameplay in my opinion. I'm not here to tell you how to run your server but rather give my personal input what I would like to see.
TE Oasis should be just a little bit longer, like 16-20 min. The classic Oasis is 20 and Oasis_TE is 15. Given a smaller map Supply is 20, Oasis should in theory at least match that. Or make both of them like 18 minutes.
Make Fuel Dump Axis spawntime just a little longer in the final phase. I take issue with Bremen also, which I too rarely see Allies win with even teams. Usually wh