Order space utilized depends on images count and attachments added. In a Android device, an image takes about 100-200 kb. In an iOS device, an image can take 500-1000 kb. If an order has 30 images, it can take 30 MB space in the memory.
If you are concerned about iOS memory space being used by the app and wish to check it, simply go to Settings > General > Storage & iCloud Usage > Manage Storage. This is Apple's article: https://support.apple.com/en-us/HT201656
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