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Your problem is likely making those API requests in a loop.  You might consider using a REST library which can support multiple concurrent calls to your end services (perhaps something based on curl_multi_exec()).  This would allow you to collapse overall API request time down to the length of whichever request happens to take the longest.

I am not familiar with Httpful which it seems you are using, but in glancing at the information available for that library, I didn't see support for making concurrent requests.  This may mean you need to change libraries or build something yourself to do this.

I will link to an example class I had once written in PHP to give you an idea for how this may be accomplished.

https://github.com/mikecbrant/php-rest-client

You are free to use it if you find it useful.