Knowing what I know now, and if there were no grid ties to plunder the cores from, i would buy the 15000w unit, and then pick up a few elcheapo 8kw or less units, and build a new enclosure, combine the transformers and just laugh.
You can find buy it now 15000units for as cheap as $1000 and less, and I have seen the 8kw units auction for $300 and less... so for $1300 in well placed bids, a really decent inverter could be cobbled together no problem... probably in the 5-6kw continuous range would be very realistic.
If you got a decent 15000w unit for the $1000 with three 5kw transformers in it ( their bigger ones.... not the smaller ones with black texta crossing out the 3kw print) you may even get by with that for almost all houses... certainly all the current off grid ones using the normal parameters.
Oddly enough, I would just use a W7 power star as a shed inverter, rather than a PJ... even though it cant be easily lowered in the idle current department, it has huge transformers that will deliver excellent performance int the sheer grunt continuous department for big machinery...ie 250amp big migs and arc welders, huge compressors, laths mills etc etc.
They were getting around for $7-800 even a few years ago. They are the same thing, but the programming is better for the huge transformers to be taken advantage of.. PJ lowers the programming to reflect their smaller transformers and less noisy fan system.. so same start power, but half the continuous power at least because of the smaller transformers.... also because of the lossy trannies, the ups function works as advertised ( inrush current on freq exhange is not high enough to bother the fets)
It is a new world for sure.... and all good fun too.
....................oztules