This is not good news.
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This isn't particularly clear.
How do they determine what are High Quality photos and videos, that won't count towards that 15GB limit.
For me does it matter if they are high or medium or low quality, they all need to be stored so 'space' is required.
In your image, it mentions "all Photos and Videos backed up before June 1st 2021 are exempt from this change and will not count towards Google Account storage."
To me that means from this date onwards your new 15GB limit starts.