I think that in the first few weeks of season 4 it will be very hard just to maintain 1500 rating.

Think about it for a second. Every 2k+ rated team will have their rating back to 1500. Some may think this just means that they boost right up to 2k again? I think not. A lot of good team will also meet each other, resulting in very good team actually will go below 1500

Arena will be very hard until some teams way below 1500 have been dispanded and restarted at 1500, and then pushing the average rating higher.