With all these amazing deals on Dell laptops popping up, I thought I might share my experience just in case it saves anyone from the frustration that I've been experienced in the last few days. I recently (less than a week ago) bought a Dell Inspiron 15" 2in1 (7506) and have been experiencing BT mouse lag similar to this. It would seem that Google is rife with similar complaints with varying effectiveness of fixes.
I've spent the last 3 days now trying to troubleshoot this and I am now at the point where I am in the process of returning it. I've updated the BIOS, tried disabling C-STATE in the BIOS, installed all the latest Windows, Dell and Intel drivers, disabled power management in device manager. Dell support initiated a remote session, checked for Dell updates, moved the mouse cursor around in circles, and went into mouse settings to change the speed of the pointer (??) and essentially weren't able to find out what was wrong (they didn't even look in device manager). Their solution was to "back up your data and do a factory reset"
Overall great sales experience and delivery, but after sales support is woeful. May have to go back to my trusty HP Spectre for awhile. Used HP support previously too and must say that I had a much better experience with them. They seemed better trained, more knowledgeable and less haphazard.
Incidentally if anyone knows the fix for this please let me know, I'd really like to get it working with this otherwise well-built laptop.
Bluetooth mouse connections naturally has high latency, some will be better than others but you should invest in a 2.4ghz wireless mouse.