Return deltas from nested values in Javascript object

I am trying to find differences between nested number values for two successive dates. My object looks like this:

obj = [
  {
    id: 'rec09SOGKDp3cgcbs',
    fields: { date: '2022-10-21T13:37:00.000Z', value: 10 }
  },
  {
    id: 'rec2PVebECpT2CG18',
    fields: { date: '2022-10-22T13:37:00.000Z', value: 25 }
  },
  {
    id: 'recF2zznFNdVkr9i8',
    fields: { date: '2022-10-23T13:37:00.000Z', value: 55 }
  }
];

And the desired output would be:

deltas = [
      {
        id: 'rec2PVebECpT2CG18',
        fields: {delta: 15}
      },
      {
        id: 'recF2zznFNdVkr9i8',
        fields: {delta: 30}
      }
    ]

I tried some of the suggestions posted here but get stuck at comparing the proper objects and the nested values. Any tips on how to structure this?