I had similar problems, and the problem lies with your wifi. Whilst the connection speed might be high you need to determine the actual download speed. Check that the HPTC and RPI2 is handing the data efficiently (No CPU or I/O waits). I slightly improved matters by buying a wifi repeater with ethernet connection, but was not totally effective.
Doing tests, with a connection speed of 98Mb I was only getting 3-6Mb download. You might improve things by buying a much better wifi dongle with extended antenna to get a better input signal - some of the small wifi dongles only have a small antenna.
Or, you could try a 5Mhz dongle if your router handles it - I believe it will work, but don't take my word for it - search on the forum for advise.
I solved the issue by buying a 1Gb homeplug (The one that connects ethernet over your home wiring)