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

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.