My wife and owned a 2014 Jayco Whitehawk 28DSBH. When we ordered it, we ordered the upgraded AC unit and insulation package. We never had any issues with staying cool inside during the summer. A fe...
Can you close off bedroom/bathroom and shut the vents to those areas? DIY improvements to insulation - vent pillows, seal holes, make sure slides are sealing well, clear plastic window covers, etc...
Upgrading to 15k btu is a marginal upgrade for significant cost.
Adding additional air/con units is problematic with only 30amp. If you aren't careful, it's really easy to overload the electrical system.