Brief Answer:
The window period for HIV is upto 3 months.
Detailed Answer:
Dear Mano567,
Welcome to HCM.
You had unprotected sex with call girl but the HIV Duos test after 1.5 years is negative so you need not to worry at all because you are absolutely safe and risk free from HIV. The window period for HIV infection varies from 15 days to 3 months. Any test after 3 months will show 100% conclusive result which is negative so don't get stressed.
As your friend I will also advice you to stay away from such unsafe sexual practices to prevent the future risk of HIV and other STDs. Allay the fear or anxiety related to HIV, calm down your self and live your life normally because you are 100% risk free. For any further query feel free to ask me again and I am here to help you out always.
Thank You