Worker and external api, make web loading very slow

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C#

web

Hi,
I have two programs:
1. a software that send data all the time to an api and the api save this data into the DB
2.a web that uses a worker that runs every 500 ms and save data into the DB

they both saves the same row, different fields

when one of them works:
the web load all the data is needed to the page like it should

when both of them works:
it takes a very long time till all the data is loaded to the page

i'm using stored procedure, and EF 6

here's the code that both worker and api are using to save data:

using (DBEntities db = new DBEntities())
           {
               var a = db.sp_SaveScale(item.GUID, item.MAC, item.CompanyID, item.Status, item.Weight, item.WeightDate, item.Active, item.Name, item.ScalesTypeID).ToList();
               if (a.Count() > 0)
                   item.GUID = (long)a.ElementAt(0);
           }

the stored procedure 'sp_SaveScale' saves all the record

what i need to do to fix the loading problem?
I need both worker and api, to work continuously

What I have tried:

I've tried delay both worker and api but still didn't help