Using 3g water for 15 lbs grain is
very thick. With that thickness, you would have difficulty wetting the grains, which would result in low efficiency. I usually use a thick mash of 1 qt per lb, but that would be 3.75g.
I'd start by getting an accurate way to measure your water. Pyrex measuring jugs are good for small amounts, but I would lose count measuring out gallons using one of them.
I have a 1 gallon container, marked in pints which is much easier. A gallon milk container would also work. You could make a dip stick for each container, and calibrate it by filling the container with carefully measured volumes of water.
For sparging, it depends how you do it.
If you fly sparge (slowly adding water to the top of the grain bed while draining out at the same rate), you need to take your time. As others have said, 60 minutes sparging for 5g is not unreasonable. For stronger beers, I have often taken 90 - 100 minutes to sparge. With fly sparging, you also need something like a false bottom that collects wort evenly across the whole of the bottom of the MLT. You could also use a manifold with cross members as mentioned in
http://www.howtobrew.com/appendices/appendixD-1.html. If you use a braid, use a long braid that meanders around the bottom of the MLT, otherwise you will get channeling.
On the other hand, if you batch sparge, the collection mechanism doesn't matter so much, and you don't need to do it slowly. With batch sparging, you drain your first runnings, then add a batch of sparge water, stir well, let is settle for a few minutes, and then drain. Some people do a single batch sparge, others do two. If you do more than one sparge, then try to get the volumes of each batch approximately equal. With batch sparging, the sugars are dissolved by the stirring of each batch of sparge water, rather than being dissolved as the sparge water gently percolates through the grain bed; so stirring the water into the grain is very important.
With good technique, there should be very little difference in efficiency between batch and fly sparging.
No matter how you sparge, it is best to get the temperature of the grain bed up to 168 - 170F. I found that this was impossible with a fly sparge unless I did a mash out by adding a gallon or so of near boiling water and stirring it in well before starting the sparge. For me, this resulted in a 10% increase in efficiency. I suspect that part of this increase was caused by having the grain bed at the correct temperature, and the rest was caused by stirring the mash out water which dissolved a lot of the sugars before starting the sparge.
Hope this helps.
-a.
I stir again at 30 minutes to break up any (I think they call them dough balls) that form, and the last batch I got 88% efficiency.
