1. you still have some time. try to see your future travel plan to combine your other trip with your passport renew
2. you just need one morning for the passport renew (not 20 days). provide self addressed return envelope so you can get your new passport by mail instead wait 15 days. choose Priority mail with trace number if not in a hurry or Overnight if in a hurry.
3. if u are in Saipan, you only have two choice for passport renew: LA out of China or where your lived inside China.
4. some time Consulate officer will visit your area, you can do the renew local (still need wait the new passpost mail to you). check China Consulate (LA) web page or call them to see if they have future scadule to visit your area.