How firm is your 15-19' length requirement? Are you trying to fit a particular parking space?
I ask because some of those trailers you are looking at with 15, 16, 17, 18, 19 in the model name are actually 20 to 25 feet long, yet you will find others with 21, 22, 24 etc in the model name that are closer the length the numbers imply. This is just one of those games manufacturers play in marketing to people who have the idea that they need to have a smaller trailer.
Many "ultra light" TTs are fairly expensive, as it takes more costly building materials and construction methods to shave off weight without too much impact on quality. When I think about low cost and light weight, I lean towards GulfStream's AmeriLite line, they've been in this market segment for at least 10 years, while it is something new for some other manufacturers.
In AmeriLite "super light" line there is a 16BHC bunkhouse with a tub, a little under 19 feet long and slightly over 3000 pounds at maximum weight. It has very little cargo capacity, and the dinette is the "adult" bed.
The other bunkhouse in the same line is 198BH, 21 feet long, about 3800 pounds maximum weight, around 3000 empty. It has a separate dinette and queen bed at opposite end from the bunks, but not sure about whether it has a tub or a walk-in shower.
Neither of the AmeriLite superlights has a slideout. Slideouts either add weight (compared to gaining the same space by increasing length) or they add a lot of cost to build the slideout at minimal weight.
Jayco came back into the low-cost lightweight market a few years ago with the Jayflight SLX line. The 154BH is just under 18 feet, about 2400 pounds empty, 3200 max weight, similar floorplan to the 16BHC Amerilite. 184BH is 20 feet long, just over 2600 empty, 3500 max weight. But it does not have a dedicated adult bed, instead it has a sofa and a dinette that converts to a bed.
I looked at the SLX models (and the Jayco captive Starcraft brand equivalents) at the RV show last fall, and was somewhat disappointed in what had been necessary to reach the low price points. The smaller examples I inspected had small window air conditioners mounted through the wall into cabinets, rather than RV air conditioners, and heaters and refrigerators were the low capacity models that normally go into pop-up campers. OK if that meets your expectations and doing occasional short trips in moderate climate destinations, but has turned out to be a problem for some buyers who thought they had found a great bargain for a RV they would use on long trips, or for full-timing or snowbird living.
If you want light weight, high quality, and the floor space gained by a slideout, you might look at the Lance TTs. Their bunkhouse model is 2185, 21.2 feet long and 4000 pounds empty, with the big roomy U-shaped slideout dinette shared by all their TT models. Lance is an example of what can be done using high quality materials well assembled using conventional panel wall construction, but these are not built to a low price point. Their bunkhouse model is likely going to be two to three times your budget. Note also, Lance does not play silly games with the numbers in their model names, being one of the few manufacturers using numbers related to actual length.
Tom Test
Itasca Spirit 29B