As far as I know the 15G, 16T, 18T & 19T all have the same turbine exducer, inducer and housing dia. therefore its just about the compressor size / downpipe / fitment etc. hence the 16T / 18T highbred options. If I’m wrong then I stand corrected, but if you can’t find a 19T bargain these other options might be worth a look.
As regards the de-cat if you have a second oxygen sensor then just feed it more oxygen so it reads base line voltage, if it doesn’t follow the lead oxygen sensor regardless if it’s a wide band (ME7) or not you won’t get a cell light, for race use only lol
