I must say the advice on here is always moving to cash, but i find that harder to then track we’re it goes.
more, go through your account for last month, how much food budget do you really need compared to what you think? are you one of those people who blithely say their weekly shop is around £80, yet ignore that top up shops add another £40 and they are catering 4-5 meals a week outside the home (be it a take away, shop bought sandwiches etc).
meal planning and online food shops might be good for you- and fully plan. Not just 7 dinners, but also lunch, breakfast, snacks, drinks. How much bread /milk /apples do you really need for a full week? (Eg, if all 4 of you are going to have sandwiches twice in a week, then do you need more than a 6 pack of bread rolls?)
when you say essentials are paid for, have you also factored extra things you need through the month, like gifts for dcs to take to parties, haircuts, dentist or opticians etc. it took me stupidly long to realise that while the cost of my dc’s swimming lesson was £30 a month, each time I had to pay to park in the car park next door which cost £2, so it was actually £38-40 a month. (Depending on how many weeks in a month.)
it could well be you don’t have £1,500 left over once all essentials are paid for, but considerably less.
stage one is to work out the real cost of your basics, then look at what’s really left over, then work out where savings could be made.