Based on the wording in your question, it is not clear if the refund identified in your amended return is an additional refund or the total refund you should have received on your tax return. When you prepare an amended return, the bottom line on the amended return is the difference between the original return and the amended return. Since your amended return identified $1,500 refund, the IRS considered that as an additional refund and that is why you received two refund checks for a total of $3,500.
When you prepare an amended return with TurboTax, it will provide the correct calculations provided you followed their amended return instructions and entered the correct data in the forms provided. If your total refund should have only been $1,500, I suspect your made an error in the preparation of the amended return and did not account for the $2,000 refund identified in your original return. You can review the data on line 18 in your 1040X amended return to see if $2,000 is reported on that line.
If the $2,000 is not on line 18, your did not enter the correct data when you prepared the amended return. If this is the case, you will owe the IRS $2,000 and they will catch this error within 6-9 months after the amended return was submitted.
Good Luck
