I'm lucky to have a space (with nothing killable behind it) in which to practice, this was at 15m but I can go up to 30m (if I don't care about having any grouping ... I'm still quite new)
What a lovely space to practice, I'm quite jealous!
Keep an eye on that bow hand grip. You want to make sure you keep a loose, open grip with the pad of your thumb pressing forward against the bow. That should be where most pressure goes.
Hand/knuckles should be at about 45° and fingers barely touching. It might help to use a finger sling to keep yourself from gripping. This helps to close up groups a lot!
Take a look at this illustration for more guidance.
