3DPrinting

Often a combination of temp too high, not enough retraction, or water contaminated filament.

If the plastic in the hot end is too hot it will keep "running" out of the nozzle after retraction and you'll get strings. Similarly if you don't retract enough to actually pull plastic out of the nozzle during a rapid move, it will want to keep pushing thru. This is supported by the little blobs it leaves on that angled surface corner its travelling to when stringing, thats excess material squeezing out during its rapid moves then being left on that wall.
And if there's water in your filament all bets are off on how it'll behave.

215 is pretty warm for that esun PLA especially if you're using the stock brass nozzle, try bumping that down to 205 or even 200, and increase your retraction speed and distance settings in prusaslicer a tiny amount (0.1mm distance, 2mm/s speed at a time until you see improvement is plenty)

Use a temperature calibration tower to test things out.

Try dehydrateding your pla first. Then try some of these other suggestions. If all else fails, these clean up really nicely with a butane blow torch.

You already got a good answer about lowering temp and tuning retraction. Other than that, you have underextrusion there (gaps in the flat part on the build plate). I think you should extend your calibration:

Calibrate temp - flow - retraction

To reduce stringing you want:

• lower temp
• higher retraction
• faster travel speed

Be careful with first two, if you go too far you might get a clog. Sometimes its just better to accept some stringing, but since you are at 215 I bet it can be improved quite easy

I can't add anything concerning stringing that the other comment didn't already cover, so I'll ask about the gaps.

Have you tried upping the flow rate to fill them in? The other option I've used in the past was lowering my Z Offset if the flow was alright.

Keep in mind that changing your flow rate will likely also cause you have to mess with your retraction settings again.

Haven't printed too much, so take my comment with a grain of salt. But I don't think the temperature is the problem. I notice that I get strings when I set my slicer to not do retraction. I guess that makes sense intuitively - strings are just plastic where they shouldn't be, and the best way to prevent that is to make sure to retract the plastic away from the print.

Also, I think 215 is slightly high, or at least higher than what I use