I'm often feel bored when I'm practicing.
Aside from what has already been said:
1) Look for inspiration in amazing performances. Take advantage of the fact that you can find a slew of performances, both by some of the best and even by amateurs who take piano to the next level. This is similar to the Lisitsa comment above (15 hrs is insane!). You're old enough to know that back in the cassette tape/record days, it was NOT easy to get a hold of a recording-- now it's just a click away.
2) Look for inspiration in new music. They don't have to be difficult, but if they are technically challenging, all the more better.
BTW, I truly believe the 25 min work followed by 5 min break (aka Pomodoro technique) is critical in practice of ANY discipline--- whether that's 20 min or 30 min or whatever you choose, the mental break is one of the biggest factors in my practice productivity, as of late.
Don't forget that everyone goes through the same struggles. So yes, apply as many 'tricks' as you can, but also know that developing a tough skin to work very hard will yield huge returns-- the tricks are just icing on the cake.