Cartography is the art of abstraction to fulfill a purpose. You may find that several simpler maps (or layers on a simpler map) are much more useful than one map with every possible thing on it. Those maps would probably be much quicker to draw, as well.

Given that you have a "realistic" map (whatever that might look like) and you want a "drawn" map (whatever that might look like):

The style and level fo detail will both be dictated by what you want to show. If terrain is critical to the purpose of the map, do lots of terrain: if terrain is mostly incidental to the purpose of the map, a few scribbles with a label that says "The Mountainiest Mountains That Are Totally Impassable Except Through This One Commonly-known Pass And This Specific Goblin Warren" convey more than many, many detailed mountain renderings. If your map is mainly about some cities/important locations and the journeys between them, then stuff at the fringes of the map away from the important elements will be far less useful and might include fanciful notes like "here be dragons" or frilly borders and artwork that depicts important story elements.

The medium in which you intend to publish your map will suggest how many pixels you need. A map for a 720p 100 dpi screen viewed at a meter away will be much lower resolution than a 1200 dpi full-color wall poster that's two meters wide. I recommend making the map a bit higher resolution than you expect that you will need because it's much easier to downsample than upsample.