Best design practice for box upload

Hello,
I have created an application to upload files directly to the box. We have around 20K users in the organization where users are uploading around 5 files in an average for the jobs that they launch. One thing we noticed is related to performance degradation due to box attachments. Generally its taking about 5 minutes to complete the whole attachment procedure including token generation,folder creation,file upload and shared link creation, Which is something not acceptable. Is there a better design guide we need to follow? Currently I'm following the below design guide

> Creating token every time when a new attachment request is being raised
>Checking for the folder if it is already exists,If not then creating the folder
>Uploading the files to box
>Creating shared link one by one for all the uploaded file during the session.

Can somebody help me to understand why there is delay for this design workflow? and what would be the possible optimization steps i can take to increase the performance? Because with this speed, Its not possible to serve this many users efficiently. Any suggestion here would be appreciated