iPhone 6 / iTunes Sync Issue

[davidjamesp]

After having synced my iPhone and iTunes for the first time, I added a handful of albums from my iTunes playlist. I had noticed many of the songs didn't fully transfer and only 3-4 songs per album synced to the phone. Now, after having deleted all songs from my "On this Phone" directory within iTunes, which now shows that it's empty, all the tracks (with a circle and red square icon) still remain on my phone despite having removed them / restarting my phone.

When deleting the tracks manually from my Music app, they seem to take 5-7 seconds each to remove, which seems a tad slow.

Is there any way to have them removed in a more timely manner?

Thanks for any help!