Don’t know the forest that well but surprised to hear it’s that long considering how quick a lap of the blue is.
R15/20/25 are about the furthest point. And the blue is a fairly direct. Maybe 20min is pessimistic, but I’d still think it’s a longer loop than the blue, you’d be going some to do it in an hour (including navigation). If you wanted to get to R15 a more interesting way, ride the blue to stickler, then turn left instead of right, it’s a shorter trail and comes out at the manhole near jump gully, up the hill to the resevoir and you’re there.
If you want a modicum of natural, find the new england switchbacks on Strava (starts in the same place as whole 9 yards), then at the bottom of the hill go straight across, the trails fairly obvious, turn right at the end onto the muddy singletrack, then spits you back out at the bottom of the hill, turn right and it’s a short climb back upto the whole 9 yards.