Fetch slows down when requesting the same url again. Why?

Question

React Native

This function sends requests to the server in my React Native app. If the request comes for the first time, the difference between start and end is minimal, and if the request goes the second and then again to the same url, or the url differs in parameters from the request that has already been, the delay is from 15 to 30 seconds approximately. In Postman, all requests go quickly. With what it can be connected?

async function request(url, method = 'GET', data, contentType = 'application/json') {
  const state = store.getState()
  const config = {
    method,
    headers: {
      'Accept': 'application/json',
      'Authorization': state.user.token
    }
  }
  if (contentType === 'application/json') config.headers['Content-Type'] = 'application/json'

  if (method === 'POST' || method === 'PATCH') {
    config.body = data
  }
  console.log('start', url, new Date())
  const response = await fetch(url, config)
  console.log('end', url, new Date())
  return await response.json()
}