it depends a lot of things, the text values are extremely small than stored images, one character value is 2 or 4 bytes. 5 mb is more than 100 keys. Common c2runtime.js could be from 100kb to 500 kb more than 2000 lines of codes. I suppose the limits could be more than 100 keys.
There is one tip, if you save X position from instance, the value would be like 20.777756466 including decimals as default, to make it shorter, you could use int() expression to convert from float to integer, the value would be 20. Don't forget sometimes JSON syntax could add more characters each one stored value.