A 15:1 compression ratio is pretty high for a single stage
centrifugal
compressor. Ingersoll Rand Centac that I worked with had a 150 psi
discharge
pressure, but got there in 4 stages. The final stage impeller was
about
6"(150mm) in diameter, spun at 22,000 rpm and cost a bundle of money.

A Pratt & Whitney PT6 turboprop engine has a hybrid compressor,
with four axial stages giving about 1.25:1 each, and one centrifugal
stage of about 10" in diameter. The whole assembly spins at around
60,000 RPM, depending on model. Diffuser pressures are on the order of
350 psi. There are smaller turboshaft engine with centrifugal impellers
of five or six inches, but they spin at speeds of about 100,000 RPM.
like a turbocharger.
The compression stage of a turbine engine requires enormous
power to drive it; for example, the Allison C250 engine used in the
Bell Jetranger helicopter has a *net* output of 420 HP, but the turbine
section is producing over 1600 hp. Three-quarters of that is required
to drive the compressor to keep the whole thing going.
Higher compressions are possible, but the machine has to be able
to take it and you need a lot of power to achieve it, just like any
piston-pounder.

Dan