That's why I said pick a better map to play on.
Dominion can easily be over in less than 20 minutes. If you want to practice combat this is the better choice. Also gold/xp is generated like on HA. So it's harder to get so far ahead you're 1v5ing the team. Even if you have to leave early you likely got more practice of combat in on this map than a whole game of SR before those 15min.
TT has a shorter distance to minions than SR. If you want to practice farming/CSing this is the better choice.
Only place SR is better is for the general feel of the map and jungling. Far as jungling goes, most of what you would practice is over before 15min.
Why should the server be loaded with your game for an extra 10-20 minutes because you started a game knowing you had to eat soon?
Again I'm not saying it's a bad idea. I could easily see your game being meaningless to the server which is hosting thousands already. But I just find it pointless. There are better options for what you're looking for.