5music has already listed A BEST -15th Anniversary Edition- Taiwan edition for preorder on their website
http://www.5music.com.tw/CDList-C.asp?cdno=437405679162
And like what Aderianu said , a pack of 6 postcards will be given as the bonus item
Also I find it interesting that cover wise , avex Taiwan utilised the Deluxe Edition Package photo & not the Regular Package photo