B787 pilot reported during pre-flight noticing the oil quality was low on both engines resulting in a call for maintenance to service the aircraft.

Narrative

During preflight; FO noticed that oil quantity showing on EICAS displayed 17 Quarts on both engines. He called Maintenance to have oil serviced as AOM Limitations section says Minimum Quantity for Dispatch is 20 Quarts INDICATED on ENG Display.Maintenance tried to tell us; it WAS serviced and there was oil in the gear box. They said it would come up when engines were started. This is NOT my experience flying this jet after X years. The maintenance personnel seemed frustrated that they would have to run the engines since the airplane had been sitting for 2 days; and the oil serviced. I advised flight attendants that they were not to board passengers while maintenance ran the engines. Maintenance NEVER notified the agents; and passengers came down the cold jetbridge as they were starting engines. FO had to run up to tell the; to stop. Passengers waited on the jetbridge in the cold and with engines running for 5-10 min before then boarding could resume.Maintenance then service the oil which was now at 15 qts. A total of 9 quarts was added to each engine and we departed with 22 qts showing on the EICAS in compliance with the AOM.Cause: Maintenance should NOT be pushing back when cockpit crews request oil servicing to stay in compliance with AOM. THEY need to coordinate with gate Agents for engine runs.Oil servicing should be done well in advance of aircraft departure especially with aircraft that have been sitting for a long time.This is the second time this week I have had this problem with oil qty not adequate and maintenance reluctant to service in compliance with AOM!!