We live in a bi level house. The basement windows are about 2 inches above ground level, and plenty big enough to escape out of in an emergency. They let in plenty of light, and we have never had a problem with leaking. Why would I need a window well? My husband seems to think we need them. ( Lived here for 8 years no problems). I've tried to add a pic. But it doesn't seem to work
If your windows have any amount of wood as part of their construction, the grade in my opinion should 8" or more below the sill, the lowest part of the window. If they are protected from the weather, all the better for where they are now, but the moisture that will always be present in the ground will eventually effect the window structure. A picture, if you can get a link posted can be added to the post by a member.
A window should last decades or longer with occasional proper maintenance. In your situation the maintenance may need to be more often. I would give the window a close look to see if there are any hairline cracks in the paint. They will appear only on close inspection.
If you do go with the window well, dig it in so the top is a few inches above grade, and place gravel inside to give any water a place to go. A 12" deep one should do what you need. Of course, you can go with an 18" too if you choose to get more clearance to the sill and more gravel in the bottom.