I'd be glad to help you transfer your QuickBooks Desktop (QBDT) 2015 data to QuickBooks Online (QBO). Since QBDT 2015 is already discontinued, I'd recommend transferring your data to any supported versions first.
Then, follow these steps to move your data into QBO. If you're using QBDT Pro or Premier, here's how to transfer your data.
Sign in as an admin to the company file you need to import.
Go to the Company menu, then select Export Company File to QuickBooks Online.
Click Start your export and sign in as an admin to your QBO company.
If you track inventory in QuickBooks Desktop: Select Yes to bring them over, then specify the as of date. You can choose No if you want to set up new items later in QuickBooks Online.
Click the Choose online company▼ drop-down list, and choose the QBO company you want to be replaced by your company file.
Select Continue and enter “Agree” in the text field, then click Replace.
Choose Yes, go ahead and replace the data and click Replace.