BX.onCustomEvent('OnBasketChange') - why does it take so long to think?

Question

1C-Bitrix

To track the event of adding a product to the cart, I use the add code

BX.onCustomEvent('OnBasketChange');

var ajax = $.ajax({
                type: 'POST',
                url: location.pathname + '?action=ADD2BASKET&id=' + tovar,
                data: {
                  ajax_basket: 'Y',
                  quantity: '1'
                }
              });
              ajax.done(function(data) {
                  BX.onCustomEvent('OnBasketChange');
              });

everything seems to be working, but he thinks for a very long time before updating the basket item counter. Tell me where to dig, or what to fix?
BX.onCustomEvent('OnBasketChange');