What is the sweep angle of the Boeing 787's horizontal stabilizers?
(Source: Boeing)
Simple image analysis shows it has higher sweep.
The general rules of empennage design can be found here (Hamburg University of Applied Sciences).

The sweep of the horizontal tailplane should be approximately 5° larger than the sweep of the wing. Thus a higher critical Mach number of the horizontal tailplane can be achieved and a loss of efficiency due to shock waves is avoided.
In addition, the lift gradient of the horizontal tailplane can be less than the lift gradient of the wing due to the increased sweep, so that the horizontal tailplane only reaches the stall state at larger angles of attack than the wing.

The main wing sweep is easily found on Wikipedia, it's 32.2°. In comparison, the stabilizer angle is 36.00° (source).


Related: How are the dimensions of the empennage determined for jetliners?