I doubt because how could the app know which must be deleted and which saved. If you have like a whole folder which needs to be deleted then it's fast but if you have like 5000 photos in one folder and then you have to select every photo you want to delete, it'll take time. One option is to create a new folder called e.g. Saved ones and then select photos which you want to save and move them to new folder (this is faster if you have a lot photos that needs to be deleted)