Welcome to the Forum!
I'm sorry to dash your hopes but you've got your answer - RSLogix 500, or a version there of. Studio 5000 Logix Designer is only for dealing with Logix 5000 controller projects. The MicroLogix controllers would be classed as Logix 500 controllers.
For the MicroLogix family of controllers the least expensive version you would require to work with a MicroLogix 1500 controller would be RSLogix Micro, which is basically RSLogix 500 with only support for the MicroLogix family of controllers (no SLC controller support).
Another option, depending on your situation, is to hire or ask someone who has the software to assist you.
If you really need to work with this controller then I would suggest you acquire this software. Are you looking to convert the program to Logix 5000?
Regards,
George