Our web uses the Salesforce API for retrieving data with this query:

SELECT id, name, CRMforNonProfit__Transactions_Total__c, Transaction_Count__c, NumberOfContacts from Campaign

The whole code looks like:
$sforce = new \SforceEnterpriseClient();
$sforceConnection = $sforce->createConnection($this->context->parameters['appDir'] . '/../exlibs/toolkit/soapclient/enterprise2.wsdl');
$login = $sforce->login($this->context->parameters['toolkit']['user'], $this->context->parameters['toolkit']['login'] . $this->context->parameters['toolkit']['securitytoken']);
$query = 'SELECT Id, Name, CRMforNonProfit__Transactions_Total__c,Transaction_Count__c, NumberOfContacts from Campaign';
$response = $sforce->query($query);

As long as we read in information about first campaign only, we observed no problems with the speed of loading. When we now also read in information about the second campaign, loading time increased to 60 seconds or more.

Where is the problem? How to speed up loading?