Question: is 7 kg a lot to lose?
Answer: A good amount to lose (sustainably) is about 0.5kg a week. So, 7kg should take around 14 weeks (though you would expect weight loss to be more rapid initially, before slowing). To lose 0.5kg a week, you should aim for a 500 calorie deficit per day to be in a deficit of 3500 calories over the 7 days.