We currently have no plans to offer a 15 gallon Infussion Mash Tun in the future. Examining optimal grist depth ratios alongside mash vessel volume requirements for popular batch sizes, we have ascertained that for the vast majority of home brewers a 15 gallon vessel is not needed.
In fact, our 10 gallon mash vessel covers virtually all typical gravity needs for 5 gallon batches as a result of zero dead space and high mash-extraction efficiency. Moreover, our 20 gallon vessels encompass the same design capabilities, yet are merely sized up for 10 gallon batches.
For 30 gallon mash tuns, we are grappling with the shear size and weight of the vessel for most home brewers. We currently don't have plans for a 30, but that could change sometime in the future.