I connect my phone to my laptop (windows 8) and initially it pairs just fine. Both my computer and phone say it is paired. After about 15 seconds my computer shows it as disconnected but my phone still says paired. When I try to send a picture from my phone to my laptop it obviously fails, even when I try to send it right away. I updated all the bluetooth drivers and I am still getting the same problem
Either your computer is shutting down that connection after 15 min's or it is your phone. It helps to know what OS the phone is running and which mfg & model of phone you are using.
Again, most likely either your phone or Windows is placing that connection into sleep mode after 15 min's. You need to check the power settings and also uncheck the power settings for the Bluetooth device in device manager.
Try a different USB cable then. Again check the power settings for USB and same for Windows power. It could be anything causing this problem. Even as I stated, the phone going into sleep/standby mode, may be sending windows a disconnect signal.
With the Bluetooth adapter if it is not a built in device. You are going to have to do some troubleshooting on your own. Since there is no way to keep guessing what is physically causing this, unless you do some work on your end to try and figure out why it is disconnecting.