Yes, both components can be upgraded - but no, Dell won't upgrade existing systems.  If you don't want to do the upgrades yourself, any local computer shop can do them for you.  
Both Dell Inspiron 15 3000 laptops too slow, about 10 mins to booth, 3 mins to before Windows opens and 2 mins to run any MS Office app. Service Tags and . Run and completed SupportAssist for both laptops couple of times but problem still persist. 
slow Dell Inspiron 15 3000