DataUtil.cls

// https://salesforce.stackexchange.com/a/376822/2984
// Efficiently checking if any fields from a list of fields have changed

public class DataUtils {
    public class Change {
        public String[] changedFields = new String[0];
        public sObject record1, record2;
        Change(String[] changedFields, sObject record1, sObject record2) {
            this.changedFields = changedFields;
            this.record1 = record1;
            this.record2 = record2;
        }
    }
    // true if any fields requested have changed
    public static Boolean hasFieldChanges(String[] fieldsToCheck, sObject firstRecord, sObject secondRecord) {
        Map<String, Object> oldValues = firstRecord.getPopulatedFieldsAsMap();
        Map<String, Object> newValues = secondRecord.getPopulatedFieldsAsMap();
        oldValues.keySet().retainAll(fieldsToCheck);
        newValues.keySet().retainAll(fieldsToCheck);
        return oldValues != newValues;
    }
    // Convenience method for checking one record change, returns empty list of fields if no change.
    // My preference is to avoid returning null values when possible, but the choice is yours.
    public static Change findFieldChanges(String[] fieldsToCheck, sObject firstRecord, sObject secondRecord) {
        Change[] results = findFieldChanges(fieldsToCheck, new sObject[] { firstRecord }, new sObject[] { secondRecord });
        if(results.size() > 0) {
            return results[0];
        }
        return new Change(new String[0], firstRecord, secondRecord);
    }
    // Returns a list of records that has at least one change, and the fields that changed
    public static Change[] findChangedRecords(String[] fieldsToCheck, sObject[] firstRecordList, sObject[] secondRecordList) {
        Change[] results = new Change[0];
        for(Integer index = 0, size = firstRecordList.size(); index < size; index++) {
            sObject firstRecord = firstRecordList[index];
            sObject secondRecord = secondRecordList[index];
            Map<String, Object> oldValues = firstRecord.getPopulatedFieldsAsMap();
            Map<String, Object> newValues = secondRecord.getPopulatedFieldsAsMap();
            String[] changedFields = new String[0];
            for(String field: fields) {
                if(oldValues.get(field) != newValues.get(field)) {
                    changedFields.add(field);
                }
            }
            if(changedFields.size() > 0) {
                results.add(new Change(changedFields, firstRecord, secondRecord));
            }
        }
        return results;
    }
}