I have two 15/30's but I already have 30 hp of low pressure air compressors.
At the speeds I'm willing to boost O2 drive gas is never a problem.
Regarding shop or LP compressors; Most of the Lowes / Harbor Freight type are optimistically rated, the HP is not "real" and the CFM delivery. Many of these lead short brutal lives.
Duty cycle is another consideration. If the compressor runs and shuts off and gets time to cool, you stand a chance. If the compressor is running all the time to keep up, short brutal life follows.
Adding receiver capacity is an effective means of reducing the duty cycle, dead compressors sitting on perfectly good tanks are surprisingly easy to find (oddly enough) This does require more space for the installation.
I'd seriously consider an electric drive gas booster. Just one apparatus to buy, install, and keep happy.