With magic tricks, anticipation is important. With Magic 2015, it’s probably not so important.
Nonetheless, if you’re eagerly awaiting Magic 2015, you can now pre-order it on Steam for £6.99. That’s the base price, for what it’s worth; there’s no discount offered for pre-ordering. What you do get for pre-ordering is a Premium Booster pack containing 10 cards that can be used in single-player or multiplayer.
If you’re super-desperate to throw even more money at Wizards of the Coast, you can also pre-order the £14.99 Magic 2015 Special Edition (which contains a soundtrack, desktop wallpapers, and “Theros: Godsend Part 1” PDF ebook) or the £26.99 Magic 2015 Complete Bundle (which contains all of the above plus 300 foil stickers and five card collections – Innistrad, Theros, Ravnica, Shandalar, and Zendikar).
Really, though, I’d suggest you wait for it to actually come out. Past Magic games have been rather variable in quality, ranging from “solid adaptation” to “horrific money-grab”; I’d wait and see which end of the scale Magic 2015 lies on before plonking down my money. It’s out on 16 July, so you’ve only got a couple of weeks to wait.