Can you please guide me if there is any way to fetch the entire inventory in one call by the store? The store has more than 7000 inventory.
That is not possible. You can read up to 100 records per API call. The throttling rate allows 1 read call per 1 second. So it will take you 70 seconds to loop through the dataset.
A more efficient way of checking inventory is to filter your API call to a timestamp equal to the last time you checked. The API will then report only items which changed since the timestamp. If you check every 15 minutes and only capture inventory which has changed during that time period you will receive a relatively small amount of data which is likely to be less than 100 records.